As with any hard disk benchmark, QBENCH results may be affected by disk-caching utilities or TSR (Terminate and Stay Resident) programs. To obtain accurate results, remove any such programs before running the benchmark.
Besides disk caching utility software, caching disk controllers may also cause the data access times reported by QBENCH to be unusually low.
Note that QBENCH is a DOS program which cannot be run under Windows or OS/2. Also, QBENCH cannot be used with drives which do not have a BIOS or INT13h interface.
To stop the benchmark prematurely during a test, press <ESC>. Do NOT stop the program by turning off the power or by restarting your computer.
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Begin Test
The left side of the dialog box contains a list of all the hard disk drives in your computer. Select the one you wish to test. After the test has completed you will have the opportunity to select another drive. B
You can also choose between the Standard
Test or the Quick
Test.
If you wish to modify the QBENCH defaults, you can specify a variety of options from the command line when you start the program. These command line options include:
Displays the command line options
Continues on error - check help before using
Specifies the drive to be tested
Specifies the number of iterations or loops
Specifies the loops multiplier for 1 sector transfers
Specifies the Sequential access percent
Specifies the Read access percent
Runs the Quick test, not the Standard test
Makes maximum block size 127 sectors
To use these command line options, exit QBENCH now and restart it with the desired options.
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QBENCH
Overview
Before
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Standard Test
The Standard test is the most accurate test. It takes longer to run than the Quick
test because it performs more repetitions of the disk operations for a more accurate measurement.
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Quick Test
The Quick test performs the same operations as the Standard
test, but doesn't use as many repetitions of the disk operations. It should complete in about 1/5th of the time of a Standard test. With most disk drives and most computers, the overall data access time calculated by the Quick test should closely match the data access time calculated by the Standard test.
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QBENCH /?
The /? option will display the complete list of command line options, along with a short description of what each option is used for.
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QBENCH /C
The /C option specifies that QBENCH will continue with the test if an error occurs while trying to read or write a sector on the hard disk. Normally QBENCH will abort the test and notify you when it encounters an error. R
QBENCH uses low-level read and write commands and may attempt to read or write sectors which were marked as bad when the drive was formatted by DOS. Thus errors reported by the benchmark do NOT necessarily indicate a problem with the drive, since the sector or sectors in question may have been removed from use during normal operation. D
QBENCH operates by reading sectors of data, and then writing the same data back to the same locations. Thus if the /C option is used and a read error occurs, the effect of writing back the possibly erroneous data is unpredictable. To be safe, always backup the data on a hard disk before running QBENCH with the /C option.
Note: the results of the test may not be accurate if you continue the test after encountering an error because the disk may spend several seconds retrying the attempt to read or write the bad sector.
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QBENCH /D:n
The /D:n options specifies that the test is to be performed on hard drive number n. For example, if n is 2 QBENCH will test your second hard drive. If the /D option is specified, the test starts immediately after QBENCH initializes without user intervention. Normally, the user selects the drive to be tested from the initial QBENCH screen.
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QBENCH /I:n
The /I:n option specifies that the Sequential Read, Sequential Write, Random Read and Random Write tests will each be performed n times for each sector size. The default is 100 repetitions. i
Note: QBENCH has been designed to generate the most statistically random request patterns for the default number of iterations used in the Standard Test. If more accurate results are required, the number of iterations should be increased significantly (to at least several hundred). Slightly increasing the number of iterations may give less accurate results.
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QBENCH /M1:n
The data access time calculation is predominantly based on the results for single sector transfers. Thus, to obtain an accurate estimate, it is necessary to perform additional iterations for the single sector measurement.
The /M1:n option specifies the extra weighting factor that should be applied for one sector disk accesses. By default, QBENCH uses a value of 4 for n, which means that instead of doing 100 iterations for each of the one sector tests, it will do 400 iterations.
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QBENCH /PS:n
The /PS:n option specifies the percentage of Sequential accesses to be used when calculating the drive's overall performance. This value is used to calculate the Weighted Average column in the detailed results as well as the overall data access time. The importance of each type of disk access is weighted by its relative frequency of occurrence in an average DOS workload mix.
The remainder of the accesses will be Random. The default percentage value for Sequential access is 65 and hence 35 percent of the accesses will be Random. The default values were obtained from studies of the access patterns of DOS (and Windows) users in their day-to-day work.
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QBENCH /PR:n
The /PR:n option specifies the percentage of Read accesses to be used when calculating the drive's overall performance. This value is used to calculate the Weighted Average column in the detailed results as well as the data access time. The importance of each type of disk access is weighted by its relative frequency of occurrence in an average DOS workload mix.
The remainder of the accesses will be Writes. The default percentage value for Read access is 60 and hence 40 percent of the accesses will be Writes. The default values were obtained from studies of the access patterns of DOS (and Windows) users in their day-to-day work.
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QBENCH /Q
The /Q option specifies that the Quick
Test should be run, rather than the Standard
Test.
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QBENCH /127
QBENCH testing has shown that certain drives and/or adapters have a problem with benchmark transfers which are 128 sectors in length (the maximum size possible). The /127 option specifies that the largest block size that should be used by QBENCH is 127 sectors rather then the default 128 sectors. Use this option if your system cannot transfer 128 sector (64K) blocks. This will not change the overall test results.
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Test Completed
The large number in the middle of the screen is the data access time which QBENCH has calculated for this drive. To see the data that was used to calculate this number, select the Detailed
Results button.
You can also compare this drive's test results with those from a variety of other disk drives by selecting the Compare
Results button.
To test a different drive, or to run the test on the same drive again, select the Test Another button. Select Exit QBENCH to exit the program and return to DOS.
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Overview
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Detailed Results
Hard Disk number is the number (1, 2, ...) of the hard disk which was tested. v
The number of Cylinders, Heads and Sectors per track for the hard disk tested is obtained by querying the test disk. }
The Size of the disk tested (in millions of bytes) is calculated from the number of Cylinders, Heads and Sectors per track. <
Test Date/Time is the date and time that the test was run.
Test Type is either Standard Test (recommended in general for accurate results) or Quick Test (to obtain quicker but less accurate results) or Custom Test if you specified, through command line argument(s), either Iterations (/I:n) or a Sector 1 Multiplier (/M1:n) value. <
The Workload Assumptions are used to calculate the Weighted Average column and the Data Access Time. The relative importance of each type of disk access is based on its frequency of occurrence from workload studies. The default workload values are 65% sequential versus 35% random, and 60% reads versus 40% writes.
Test Loops refers to the number of disk commands which are executed and timed for each block size and type of disk access. In the default case for the standard test, 100 loops or iterations are used.
The access time calculations are based largely on the command service time for a transfer size of one sector. Thus additional iterations for this measurement are necessary to obtain an accurate data access time value. The Sector 1 Multiplier indicates how many times more loops will be executed for single sector transfers than for other transfer sizes. In the default case the Sector 1 Multiplier is 4 indicating that 400 iterations, rather than 100, will be used for this case. i
The Test Results show the average time in milliseconds to perform transfers of eight different lengths.
The Block Size (Sectors) shows the size of each transfer in 512-byte sectors. A complete test is run for each block size which is a power of two (i.e., 1, 2, 4, 8, 16, 32, 64 and 128 sectors), since these sizes are of most interest.
For each block size tested, the average Command Service Time for each of the four types of disk access (Sequential Read, Sequential Write, Random Read and Random Write) is calculated and displayed. The command service time is the average total time to complete a read or write command. The Weighted Average column is calculated from the other four columns using the percentages from the workload assumptions.
The Access Time displayed at the bottom of each column is calculated by taking the command service time for a transfer of one sector and subtracting the transfer time for one sector.
The Weighted Average of the four access times is the Data Access Time in milliseconds. This is the single performance index which describes the performance of this disk drive for the given workload mix. &
Data access time is a comprehensive index of drive performance which can be used for drive comparisons. For example, if drive A has a data access time of 10 ms and drive B has a data access time of 13 ms, then drive A can be said to be 30% faster than drive B for an average DOS workload mix.
Finally, the Transfer Rate is calculated from the slope of the weighted average line when command service time is plotted against transfer size. The slope is the time in milliseconds to transfer one sector, and the transfer rate is obtained by converting this value to KBytes/second.
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Overview
Compare
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Compare Results
This section presents the data access times, as measured by QBENCH, for a variety of disk drives. The drives in the list are sorted in capacity order. The list contains primarily Quantum drives, but drives from other manufacturers are included for comparison. The entire list of drives and their data access times can be either Printed or Saved to a file by selecting the appropriate choice.
The drive just tested is displayed in the middle of the screen, with drives in the same general size category included on the screen for comparison. The data access time entry for each drive in the list is based on an actual QBENCH run for that drive. For every drive in the table, including the drive just tested, complete detailed results are available by moving to the drive of interest and selecting Detailed
Results. j
For more information on interpreting the comparative database, please refer to the QBENCH documentation.
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Detailed
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Test Progress
The main portion of this screen is a graphical representation of the disk drive being tested. Its purpose is to illustrate which portions of the drive are being accessed.
The Test Information area describes both the current type of disk access that is being performed and the size of the read/write operations (in 512-byte sectors). ;
You can press the <Esc> key to halt the test at any time.
Note: When you exit from these help screens, the test will resume. The interruption to view the help screens will not affect the accuracy of the results.
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QBENCH Overview
QBENCH performs a total of 32 different complete tests (each of the four different types of disk access for each of eight different transfer sizes). The access types are sequential read, sequential write, random read and random write. The transfer sizes are 1, 2, 4, 8, 16, 32, 64 and 128 sectors, where a sector is 512 bytes of data. .
For both sequential and random access, the read and write tests are interspersed. In either case, the same data which is read during a read test is written back to the location from which it was read during the corresponding write test. In this way data on the disk is not disturbed by the benchmark.
Low-level disk requests (called BIOS or INT13 requests) are used to allow random and sequential measurements across the disk without regard to where data is stored on the disk. DOS file system overhead and issues such as file fragmentation are avoided with this approach.
Multiple-zone recording, a feature common to modern disk drives, allows more sectors of data to be stored on the outer tracks of a disk (where there is more room) than on the inner tracks. This feature causes the off-the-disk transfer rates to vary depending upon where on the disk the data is located. QBENCH takes multiple-zone recording into account by dividing all sequential tests into four parts. Two of the tests are performed on the outermost and innermost tracks, while the other two are equally spaced in between. This allows the benchmark to get a representative sampling of track densities for drives which employ multiple-zone recording. =
Random tests are also done in four parts, for convenience. This also allows QBENCH to update the screen at least four times during a test, to indicate test progress, without affecting the timing of the disk requests being measured. All screen updates take place between test segments when no timing is taking place.
While the test is in progress, a map of the drive layout is provided so that the user can see exactly where on the disk requests are being executed. Map information, including the size of each block in the map, is provided in the lower right box entitled Map Information.
By observing the map, the user can first watch the four evenly spaced sequential tests for a given transfer size, with the read portion of each directly followed by the write. The random tests for that transfer size follow in a similar manner. The same amount of data is transferred in each test, although the sequential tests appear to transfer less, since several sequential transfers occur in each display block in the map while random transfers are typically one per block.
The lower left box entitled "Test Information" shows exactly which test is being executed, and what percentage of that test has been completed. The test type and block size are displayed, along with the percentage complete.
The overall progress of the test is displayed at the bottom of the screen. A total of nearly 50 MBytes of data is transferred when the standard test is run. As the test progresses, the bar at the bottom of the screen shows the percentage of this total which has been completed. In terms of data transferred, the test runs more quickly at higher block sizes, so the bar provides a conservative estimate of the percentage of the total test time which is complete.
To pause or abort the test while it is running, press the <Esc> key. The user can resume benchmark execution without affecting the accuracy of the results.
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Completed
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Erroneous Results
For certain drives, particularly older technology drives with an interleave factor greater than one-to-one, the mathematical model which is the basis of the access time calculation is not correct. This does not mean that there is any problem with the drive itself or its operation. It only means that the data access time calculation procedure used by QBENCH does not apply.
Asterisks are printed for any access times with this problem. Asterisks are also printed for data access time, since it is calculated from the other access time values. n
Only the access time calculation is affected. All other values which are printed for this drive are correct.
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Disk Error
This message indicates that a disk error has occurred during QBENCH testing. R
QBENCH uses low-level read and write commands and may attempt to read or write sectors which were marked as bad when the drive was formatted by DOS. Thus errors reported by the benchmark do NOT necessarily indicate a problem with the drive, since the sector or sectors in question may have been removed from use during normal operation. v
QBENCH has a /C command line option which instructs the benchmark to continue the test in the event of a disk error. D
QBENCH operates by reading sectors of data, and then writing the same data back to the same locations. Thus if the /C option is used and a read error occurs, the effect of writing back the possibly erroneous data is unpredictable. To be safe, always backup the data on a hard disk before running QBENCH with the /C option.
If the disk error occurs during the part of the test which transfers data 128 sectors at a time (i.e., the block size is 128 sectors when the test fails), it may be possible to run QBENCH successfully by invoking the /127 command line switch when the benchmark is first invoked.
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]iled
Results button.
You can also compare this drive's test results with those from a variety of other disk drives by selecting the Compare
Results button.
To test a different drive, or to run the test on the same drive again, select the Test Another button. Select Exit QBENCH to exit the program and return to DOS.
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Detailed Results
Hard Disk number is the number (1, 2, ...) of the hard disk which was tested. v
The number of Cylinders, Heads and Sectors per track for the hard disk tested is obtained by querying the test disk. s
The Size of the disk tested (in millions of bytes) is calculated from the number of Cylinders, Heads and Sectors. <
Test Date/Time is the date and time that the test was run.
Test Type is either Standard Test (recommended in general for accurate results) or Quick Test (to obtain quicker but less accurate results) or Custom Test if you specified (through command line argument(s), either Iterations (/I:n) or a Sector 1 Multiplier (M1:n) value(s). <
The Workload Assumptions are used to calculate the Weighted Average column and the Data Access Time. The relative importance of each type of disk access is based on its frequency of occurrence from workload studies. The default workload values are 65% sequential versus 35% random, and 60% reads versus 40% writes.
Test Loops refers to the number of disk commands which are executed and timed for each block size and type of disk access. In the default case for the standard test, 100 loops or iterations are used.
The access time calculations are based largely on the command service time for a transfer size of one sector. Thus additional iterations for this measurement are necessary to obtain an accurate data access time value. The Sector 1 Multiplier indicates how many times more loops will be executed for single sector transfers than for other transfer sizes. In the default case the Sector 1 Multiplier is 4 indicating that 400 iterations, rather than 100, will be used for this case. i
The Test Results show the average time in milliseconds to perform transfers of eight different lengths.
The Block Size (Sectors) shows the size of each transfer in 512-byte sectors. A complete test is run for each block size which is a power of two, since these sizes are of most interest.
For each block size tested, the average Command Service Time for each of the four types of disk access (Sequential Read, Sequential Write, Random Read and Random Write) is calculated and displayed. The command service time is the average total time to complete a read or write command. The Weighted Average column is calculated from the other four columns using the percentages from the workload assumptions.
The Access Time displayed at the bottom of each column is calculated by taking the command service time for a transfer of one sector and subtracting the transfer time for one sector.
The Weighted Average of the four access times is the Data Access Time in milliseconds. This is the single performance index which describes the performance of this disk drive for the given workload mix. &
Data access time is a comprehensive index of drive performance which can be used for drive comparisons. For example, if drive A has a data access time of 10 ms and drive B has a data access time of 13 ms, then drive A can be said to be 30% faster than drive B for an average DOS workload mix.
Finally, the Transfer Rate is calculated from the slope of the weighted average line when command service time is plotted against transfer size. The slope is the time in milliseconds to transfer one sector, and the transfer rate is obtained by converting this value to KBytes/second.
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Overview
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Compare Results
This section presents the data access time, as measured by QBENCH, for a variety of disk drives. The drives in the list are sorted in capacity order. The list contains primarily Quantum drives, but drives from other manufacturers are included for comparison. The entire list of drives and their data access times can be either Printed or Saved to a file by selecting the appropriate choice.
The drive just tested is displayed in the middle of the screen, with drives in the same general size category included on the screen for comparison. The data access time entry for each drive in the list is based on an actual QBENCH run for that drive. For every drive in the table, including the drive just tested, complete detailed results are available by moving to the drive of interest and selecting Detailed
Results. f
IMPORTANT: Data access time, as well as the detailed data used to calculate it, has several sources of variation which should be kept in mind when interpreting these comparative results. The user should not necessarily expect test results to be identical to those in the table, even for the same drive model. In other words, your results can and will vary. ;
The first source of variation is in the drive itself. Drives are complex electromechanical devices, with many components which are subject to some variation. Many of the entries in the comparative table represent measurements for a single drive only, which should be typical of drives of that particular model although individual drives will vary slightly. In addition, changes in the firmware which controls drive operation can affect the data access time. Since firmware is upgraded occasionally, the access time for a given drive model may change slightly over time.
In addition, the intense nature of the I/O generated by QBENCH may significantly change the operating temperature of the drive, particularly if it was brought up from as cold start right before running the test. Such a temperature change may in turn trigger what is called a thermal recalibration in some drives. Depending upon the point during the test at which it occurs, a recalibration can also significantly affect the results.
The second important source of variation in results is due to the host CPU type and speed, and the I/O bus implementation of the test machine. In particular, the command service time values, which make up the majority of the detailed results, include transfer time, which, along with the data transfer rate, is highly system dependent. CPU speed can change transfer rates and times by a factor of two or more from a slow machine to a fast one.
The data access time measure is designed to be as system-independent as possible. However, certain drives still show a variance from one system to another. Nearly all data in the comparative table was gathered on a Compaq DeskPro 386/33 MHz computer. A few drives which could not be installed using their full drive capacity on the Compaq DeskPro were run on a comparable IBM-compatible computer with a BIOS allowing programmable drive types. _
A final source of variation is due to the test itself. The magnitude of this effect for a given system and drive can be observed by running the test multiple times and observing the differences. Statistical variation should be expected in any measurement. For benchmarks like QBENCH, timing accuracy is a particular reason for statistical variation. E
To obtain a completely valid performance comparison of two drives, run the tests on the particular system for which they are being evaluated. Besides testing the drives on the same system, be sure that the test procedure is identical in both cases so that both drives are being evaluated under exactly the same conditions. M
The objective of including a comparative database in QBENCH is to give the user an idea of the relative performance of a sampling of different drives. This data is included strictly for information purposes for the interested user. No guarantees should be implied about the performance of any drive based on the data in this table.
Note: since all tests were run on an IBM-compatible PC/AT system, the results for any SCSI drives in this table necessarily include the additional overhead necessary to translate drive requests to SCSI commands. Due to this extra command overhead, the data access time for a SCSI drive can be expected to be approximately two milliseconds higher than that for the AT version of the same drive.
SCSI results may show additional variation based on the SCSI host adapter used. All Quantum SCSI drives in the table were tested using a Future Domain FD-1660 host adapter. Other SCSI drives were tested using their own adapter if applicable.
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Test Progress
The main portion of this screen is a representation of the disk drive being tested. Its purpose is to illustrate graphically which portions of the drive are being accessed.
The Test Information area describes the current type of disk access that is being performed as well as the size of the read/write operations in sectors. A sector is 512 bytes. ;
You can press the <Esc> key to halt the test at any time.
Note: When you exit from these help screens, the test will resume. The interruption to view the help screens will not affect the accuracy of the results.
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QBENCH Overview
QBENCH performs a total of 32 different complete tests (each of the four different types of disk access for each of eight different transfer sizes). The access types are sequential read, sequential write, random read and random write. The transfer sizes are 1, 2, 4, 8, 16, 32, 64 and 128 sectors, where a sector is 512 bytes of data. .
For both sequential and random access, the read and write tests are interspersed. In either case, the same data which is read during a read test is written back to the location from which it was read during the corresponding write test. In this way data on the disk is not disturbed by the benchmark.
Low-level disk requests (called BIOS or INT13 requests) are used to allow random and sequential measurements across the disk without regard to where data is stored on the disk. DOS file system overhead and issues such as file fragmentation are avoided with this approach.
Multiple-zone recording, a feature common to modern disk drives, allows more sectors of data to be stored on the outer tracks of a disk (where there is more room) than on the inner tracks. This feature causes the off-the-disk transfer rates to vary depending upon where on the disk the data is located. QBENCH takes multiple-zone recording into account by dividing all sequential tests into four parts. Two of the tests are performed on the outermost and innermost tracks, while the other two are equally spaced in between. This allows the benchmark to get a representative sampling of track densities for drives which employ multiple-zone recording. =
Random tests are also done in four parts, for convenience. This also allows QBENCH to update the screen at least four times during a test, to indicate test progress, without affecting the timing of the disk requests being measured. All screen updates take place between test segments when no timing is taking place.
While the test is in progress, a map of the drive layout is provided so that the user can see exactly where on the disk requests are being executed. Map information, including the size of each block in the map, is provided in the lower right box entitled "Map Information".
By observing the map, the user can first watch the four evenly spaced sequential tests for a given transfer size, with the read portion of each directly followed by the write. The random tests for that transfer size follow in a similar manner. The same amount of data is transferred in each test, although the sequential tests appear to transfer less, since several sequential transfers occur in each display block in the map while random transfers are typically one per block.
The lower left box entitled "Test Information" shows exactly which test is being executed, and what percentage of that test has been completed. The test type and block size are displayed, along with the percentage complete.
The overall progress of the test is displayed at the bottom of the screen. A total of nearly 50 MBytes of data is transferred when the standard test is run. As the test progresses, the bar at the bottom of the screen shows the percentage of this total which has been completed. In terms of data transferred, the test runs more quickly at higher block sizes, so the bar provides a conservative estimate of the percentage of the total test time which is complete.
To pause or abort the test while it is running, press the <Esc> key. The user can resume benchmark execution without affecting the accuracy of the results.
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Limitations
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QBENCH Theory
This section contains advanced information concerning the derivation of data access time and may be beyond the level of interest of the average user. @
Definitions: (1) Command Service Time is the total time that it takes to complete a read or write command. (2) Access Time is the time from the issuance of a read or write command until the desired data is located but not transferred. (3) Transfer Time is the time it takes to transfer data once it has been accessed.
For all access types (sequential read, sequential write, random read and random write) the relationship between the transfer size (amount of data transferred per request) and the command service time (the time to complete a read or write command) is highly linear for all drives.
Command service time is equal to access time plus transfer time. Access time is the fixed or constant portion of command service time, while transfer time is proportional to the amount of data transferred. 7
Access time cannot be measured directly, since all disk operations involve data transfer as well as access. The value closest to access time which can be measured is the command service time for a single sector (this service time includes the transfer time for a single sector in addition to the access time). y
Access time is calculated by subtracting the transfer time for one sector from the command service time for one sector.
The transfer time for a single sector (transfer time per sector) is equal to the slope of the line when command service time is plotted against transfer size. _
To calculate access time: (1) measure the command service time values for several transfer sizes; (2) calculate the slope of the best fit straight line for command service time vs. transfer size - this slope is the transfer time per sector; (3) calculate the access time by subtracting the transfer time from the command service time for one sector.
Definition: Data access time is the weighted average of the access times for each access class, where each access time value is weighted according to the frequency of occurrence of that class in a typical DOS user workload mix.
Once each of the access times have been calculated, the data access time can then be calculated based on the workload mix percentages. W
The data access time calculation, as well as each entry in the Weighted Average column in the output, is calculated from the individual values for the access types as follows. The default workload values are 65% sequential (with 35% random), and 60% reads (with 40% writes). To find the exact weighting factor for a given access type, multiply the appropriate workload percentages. For example, for sequential read, use .65 for sequential, times .60 for read, which equals .39 or 39%. Applying this formula, other values are 26% for sequential write, 21% for random read, and 14% for random write.
The slope of the line when command service time is plotted against transfer size is the average time to transfer a sector in milliseconds. The data transfer rate displayed is calculated from the slope of the weighted average line. The calculation goes as follows. If the slope is .40 ms per 512 byte sector (for example), the complete transfer rate formula would be (512/1024)/(.40/1000) = 1250 KB/sec. The 1024 converts bytes to KBytes, and the 1000 converts milliseconds to seconds.
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Limitations
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Data Access Time Limitations
Data access time is designed as an improved measure of disk drive performance in single-user DOS and Windows systems. A workload-weighted measure of drive access time, it provides a comprehensive index which describes the performance that a typical user will experience. However, there are limits to the applicability of data access time beyond the DOS systems for which it was designed. p
Other operating systems, even on PC-compatible computers, would certainly have different workload assumptions on which their data access time calculations would be based. Each workload mix would have to be determined individually for each operating system with a representative workload study. Measurement tools would have to be developed to take these measurements. 1
Benchmark measurements for other hardware platforms could be significantly different than the results for PC-compatible computers. Bus implementation and I/O architecture would certainly have an effect on the raw measurements, and the data access time values calculated could be quite different as well.
Note that data access time is designed to measure the access speed of the drive mechanism; it is important to disable system caching to accurately do this. File servers typically make heavy use of caching to achieve high levels of I/O performance. Thus data access time is not appropriate as a measure of file server performance, although with the right workload assumptions it could indicate which drives might function most effectively on a particular server.
Although new disk drive technology which has an effect on access time is captured in the data access time measure, still more advanced, higher-level new features are not. For example, the effect of retaining Least-Recently-Used data in multi-segmented caches such as those implemented on all on Quantum drives is not shown by this benchmark. The effect of prefetching data into a particular cache segment is captured, however.
As another example, QBENCH will show no performance advantage for drives with the SCSI command queuing feature. This feature allows queuing and access time optimization for multi-user systems by allowing the drive to reordering requests to minimize seek time and latency.
Drive array subsystems provide another example of systems for which the data access time measure is not likely to be appropriate. Drive arrays achieve improved performance through using several drives in parallel, while QBENCH measures data access time only for individual drives.
In summary, data access time provides a single number which describes the performance of a drive on DOS and Windows single-user systems. This number should not be used as the indicator of drive performance for systems and situations beyond those for which it was designed.
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THelpTopic
Erroneous Results
For certain drives, particularly older technology drives with an interleave factor greater than one-to-one, the mathematical model which is the basis of the access time calculation is not correct. This does not mean that there is any problem with the drive itself or its operation. It only means that the data access time calculation procedure used by QBENCH does not apply.
Asterisks are printed for any access times with this problem. Asterisks are also printed for data access time, since it is calculated from the other access time values. n
Only the access time calculation is affected. All other values which are printed for this drive are correct.
THelpTopic
Disk Error
This message indicates that a disk error has occurred during QBENCH testing. R
QBENCH uses low-level read and write commands and may attempt to read or write sectors which were marked as bad when the drive was formatted by DOS. Thus errors reported by the benchmark do NOT necessarily indicate a problem with the drive, since the sector or sectors in question may have been removed from use during normal operation. v
QBENCH has a /C command line option which instructs the benchmark to continue the test in the event of a disk error. N
WARNING: QBENCH operates by reading sectors of data, and then writing the same data back to the same locations. Thus if the /C option is used and a read error occurs, the effect of writing back the possibly erroneous data is unpredictable. To be safe, always backup the data on a hard disk before running QBENCH with the /C option.
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