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M.u.C.S. Disc 2000
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question.txt
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1997-01-21
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Questions and Answers about GEMAR:
Q: Why does it sometimes take so much time to read an index from a tape?
A: For reasons of data safety GEMAR stores the index behind the backup.
This is necessary to protocol a potential error that may have
occured during the storing procedure. The error will be protocolled with
the index. In order to provide a quick access to the index GEMAR also
puts an index in front of the data. It will later be remarked within
GEMAR.KEY, whether the index is valid.
If the index in the front is not valid during restoring the second one
will be read. This might take a while.
Q: Why does my streamer sometimes winds the tape backwards and forwards
a few inches?
A: If the computer is not fast enough to provide the streamer with data,
the streamer stops until the computer supplies the next data. But since
a streamer works quite fast there would be large gaps in between the
data. Thus, the streamer rewinds the necessary tape: unfortunately, this
takes quite some time.
With GEMAR this is suppose to happen very seldom. However, the size of
the buffer and the data rate should be matched as well as possible.
Q: Why does my streamer stops sometimes during a backup?
A: Unfortunately it is not possible to read the data from the hard disk as
fast as necessary in order to meet the requirements of the streamer.
Therefore, GEMAR fills up its' buffer storage before the data will be
written on the streamer. Meanwhile the streamer has to wait.
Q: Why am I not able to safe the occupied sections of my hard disk?
A: GEMAR was designed to provide maximum data protection. Therefore
it makes more sense to read the files from the hard disk through the
system. Due to this, data saving is not a problem for GEMAR, even with
a new and expanded data format on a hard disk. As long as the data can
be used from the desktop, also GEMAR is able to save them.
sinnvoll die Dateien von der Festplatte nur über das Betriebssystem
Q: Why are the flags 'Load to Fast-RAM' and 'Allocate Fast-RAM' not set
within GEMAR?
A: If GEMAR would be driven by a streamer connected with the DMA-Port of
the TT, the data had to be sent to an intermediate buffer before they
would be sent to the streamer. GEMAR does not support this option as it
would take too much time.
If the streamer is hooked on to the SCSI-Port of the TT the flags can
turned on.
Q: Why can I not select the streamer icon, if the index was read from the
hard disk?
A: I can only read one index from the hard disk or the tape. Therefore,
the streamer can not be selected after having read a hard disk index
and vice versa.
Q: Why is GEMAR not able to put its' desktop into a window? This is quite
bothering under MultiTOS/MultiGEM/Mag!X.
A: That's simple: Basically GEMAR runs within a Multi-Tasking-System. But
it is quit dangerous to make backups under Multi-Tasking while other
programs may change data on the hard disk. Because of that GEMAR should
always run alone - it can then keep its' own desktop.
Q: Why can I make no Image-Backup of the enire hard disk?
A: The proble is that you can not simply determine the size of the hard
disk. If 'Mode-Sense' is used the correct value will not always be
obtained while using 'Read-Capacity' does not work with every hard disk
and SCSI-adapter.
Q: Why can I not simply pull a disk station icon on the streamer icon
in order to save the data?
A: During the restore process it would not be absolutely sure, whether the
data shall be stored in their original paths, or in a different path.
Also, if a backup would be made it will not be clear, whether it is
going to be a Full-, Daily-, or Incremental one.
This is the reason why the 'pull icon' function is not implemented.
Q: Do I have to delete the tape before making a backup?
A: Actually this is not necessary. A conventional SCSI-streamer works such
that the entire tape will be deleted before writing on it - starting
from the very beginning. However, there are some exotic streamers on
the market which makes it necessary to delete the tape explicitly before
one write on it.
Q: Why will there be always 4 hard disk stations declared for the streamer?
A: Some hard disk driver check the existence of a changeable medium of a
SCSI-machine. In this case the driver assumes that it is a changeable
hard disk and announces 4 partititions. Therefore, a medium which will
be put in later, can also be used. Of course this is not suppose to
happen too often. This makes it necessary to configure the disk driver
in a way that the streamer will not be recognized.
For AHDI the best is to use the program HDPATCH. Also the SCSI-address
with the streamer must be cancelled (Options, CUSTOM SCSI/ACSI). If you
use HUSHI please take the program SCSITOOL and select 'Driver/Configure'
(or CONTROL-K) within the menu. A dialog box appears which asks you to
choose a 'Sequence of Machines'. Afterwards you will be in a another
dialog box, where you are suppose to cancel your streamer address (click).
Finally step back with 'OK' twice and answer 'yes' to 'Save Settings in
HUSHI.SYS?' - ready!
Q: How can I find the necessary parameters for my streamer in the easiest way?
A: Me personally made good experiences with the following procedure:
-Set buffersize equals the value which is given in the streamer manual
(consider possible deduction)
-data rate equals the value of the streamers + 25 %
-time before SCSI off
-Wait before/after SCSI unchanged
-Verbose on
-Make a backup. The data rate is too small if the streamer stops as long
as the buffer beam is not equal zero. Try a lower data rate, if the
buffer drains empty all the time.
-You should also have a closer look on the behavior of the 'wait vor/nach
SCSI'. The values at the TT should actually be adjustable to zero.
Otherwise, jsu turn it on zero and check if there are any errors
occuring. Will there be an error message by GEMAR (CommandTimeout) 'Wait'
must be turned up before SCSI. Will there be etv_crit (Data on disk) as
error message 'Wait' must be turned up after SCSI.
'Wait'
-Under certain circumstances a value for Wait after SCSI which is too
small may result of necessary retries of the hard disk driver. This
can be seen by a sudden drop in data rate.
Generally it is a matter of patient to find the right parameters.
If it should not work to keep the streamer on streaming, you should set
the buffer size at zero. With this, a segment as large as possible will
be filled up before it is sent to the streamer.
Q: Assume, I make a restore of disk drice C:; afterwards I will do the same
with disk drive D:. - Does the streamer always rewind, before it restores
the data of diskdrive D:. Why does it do that ?
A: Because of the particular buffer strategy of GEMAR, the tape will already
be in the data range of disk drive D:. Unfortunately not all streamers
are able to master a "space backwards". Thus, the tape needs to be
rewinded, so that the correct location can be found from the beginning.
Q: After having reconfigured my hard disk (= reorganizing the partitions),
GEMAR always uses the index in the back. Why does it not take the one
in the front position which would actually be the correct one?
A: The file GEMAR.KEY contains the key for using the index in the front for
carrying out this backup. In case of a reconfiguration of the hard disk,
the file should be stored on an external disk. With this, the
key for this backup will be available during restore.