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wrote in message
om...
Hi,

scsi reserve/release driver flag is normally set in Unix environment.
That means that
the tape driver reserves each tape device during an open I/O control
and release it with scsi-command "release unit" during I/O close
process. This procedure makes sure that only one server/application
can communicate to a drive at a time.

For sure, this flag should be reset in cluster environment due to the
fact that any operating cluster node can crash anytime during w/r
operations without releasing that drive. If that happens, no other
cluster node would be able to talk to that drive, well, Legato inquire
would work fine, but any other tape I/O should be rejected with scsi
status "busy".

I'm now wondering, if it is a good advice to reset that flag also in
shared tape environment (like Legatos DDS or Veritas Master/Media
Server concept),

any comments?


Running without reserve/release means any machine can start talking to the
tape device. Nothing stops node A from sending a 'mt -f /dev/rmt/0 rewoffl'
while node B is running a backup. The entire purpose of reserve/release is
to prevent such mishaps.

If a cluster node crashes and another node takes over, it will be the
responsibility of that node to reset all peripherals it now controls to a
known state. If the tape drive is reserved by the crashed node, the
surviving node can send a SCSI reset to lift the reserve condition.

In a shared storage environment this may be unwanted behaviour, in that case
a node can use persistent reservation to keep a device tied to a certain
node, regardless if it's up or crashed.

Rob