Im sending the response to the list as Im getting queries about what
exactly SCSI reserve/release is.

The SCSI protocol has a feature to arbitrate access to a device at
the SCSI level. It does so using SCSI reservations. When a device
wants to open a SCSI device it first attempts to obtain a reservation.
If the device is in use, the attempt will fail with busy. The host may
however
force a reservation by sending a target reset, causing the device to
release its reserve, and allowing the host to attempt another reserve.
The reset is "last resort" tactics. Bearing in mind, some tape drives
rewind on reset.

The setting is discussed lightly in 3.4 manuals for Solaris. I dont see a
mention
for other platforms media servers. In particular it talks about disabling
reserve/release in st.conf. It also refers to an old version of Solaris 2.5
and
an st patch.

We are currently running without reserve/release and have experienced
arbitration issues. We have seen media been overwritten and corrupt
media labels. We have seen media servers not agreeing as to what each
drive is up to or what tape is in the drives.

Based on our own analysis It seems if you disable reserve/release, only SSO
is in
control of arbitration to drives. However, SSO does not seem to arbitrate
access
to devices outside of netbackups command set, thus a tar, mt, dd against rmt
devices will cause unpredictable results.

Its unclear then, from the manuals, whether disabling SCSI reserve/release
is
really what we should be doing. Given, in a large scale SAN environment with
many media servers, its very difficult to tell whos doing what to the tape
drives
via Solaris command set. In addition, SAN is hetrogeneous. Do we disable
reserve/release in NT/AIX/True64? Theres no mention of this anywhere.

Thats what prompted the original email. Ive discussed the issue with Veritas
to death. Th responses I get are inconsistent depending on who you talk to.
I wanted to hear from real life examples.

Regards
Peter Marelas



> -----Original Message-----
> From: Jason Ahrens [ahrensj AT psi DOT ca] [SMTP:AhrensJ AT psi DOT ca]
> Sent: Tuesday, 17 April 2001 1:07 AM
> To:   Veritas BU
> Subject:      RE: [Veritas-bu] SCSI Reserve/Release
> 
> Out of curiosity (as I am using these same drives) what is this
> Reserve/Release?
> 
> Jason
> 
> -----Original Message-----
> From: Marelas, Peter [mailto:MarelP AT AUSTRALIA.Stortek DOT com]
> Sent: April 16, 2001 08:00
> To: 'veritas-bu AT mailman.eng.auburn DOT edu'
> Subject: [Veritas-bu] SCSI Reserve/Release
> 
> 
> Hi,
> 
> I'ld like to take a poll on how many installations of Netbackup 3.2GA or
> 3.4
> in a Fabric Switched SAN environment
> with Shared Storage Option, have enabled SCSI Reserve/Release in the
> Solaris
> st driver (st.conf).
> 
> Please let me know if you have a similar environment and whether you
> enabled
> reserve/release.
> Also, I would be interested to hear of any problems experienced if
> reserve/release is NOT enabled, and if
> reserve/release IS enabled.
> 
> Peter Marelas
> Senior Consultant
> 0410 497 228 Mobile
> 61.3.9699.1033 Phone
> 61.3.9690.8528 Fax
> StorageTek
> INFORMATION made POWERFUL
> 
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