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HOWFASTI.SIT
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2000-06-30
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46 lines
Two questions are of concern regarding the execution time of BUSH:
1) How long does it take to back up my files?
2) How much longer does it take if I use the read-after-write CRC
checking?
The times given below were obtained on the following hardware:
Computer: SB180FX - 6.144 MHz HD64180
BDOS at 0c006h, giving an I/O buffer of 332 sectors (41.5K bytes).
Source Drive: ST225/Xebec 1410A, 4K allocation blocks
Destination Drive: Mitsubishi 4853 DSDD 80-track 5-1/4" floppy, SB180-2 format
(782K bytes), 2 ms step rate, 2K allocation blocks
Times for the extremes: Without read-after- With read-after-
write CRC checking write CRC checking
1 file of 782K 5 min 15 sec 14 min 45 sec
195 files of 4K each 21 min 43 sec 34 min 40 sec
(780K total)
For something a little closer to normal ('normal', or course, being defined
as whatever I happen to have on MY disk at the time--your mileage will vary):
91 files totaling 776K 10 min 19 sec 18 min 56 sec
(average 8.5K each)
(All times were measured by hand, from the 'Floppy disk empty, continuing...'
message until the bell sounded when the floppy filled, and are rounded to the
nearest .5 sec).
So, not surprisingly, large files transfer faster than small ones (less
running back and forth between the directory tracks and the data tracks).
However, adding CRC checking to these files makes the backup take 2.8 times
as long, where doing the same to backups of very small files only adds 59% to
the run time. On the 'average' file sizes, the increase is a factor of 1.83.
The reason for this variation is not immediately obvious, although it may
have to do with the time to calculate the CRC on small files relative to disk
rotational latency and sector skewing, and therefore be very dependent on the
particular hardware and disk format in use. I would like to hear comparison
times on other systems/hardware, especially on the differences between
non-verifying and verifying backups.