Networker

Re: [Networker] clustered storage nodes installation

2003-06-30 13:53:22
Subject: Re: [Networker] clustered storage nodes installation
From: Jose Quinteiro <jquintei AT LEGATO DOT COM>
To: NETWORKER AT LISTMAIL.TEMPLE DOT EDU
Date: Mon, 30 Jun 2003 10:51:49 -0700
Hello,

It's important to note that SCSI-2 reserve/release will not prevent
tapes from being rewound if a bus reset happens. It will only prevent
other hosts from accessing a tape that is in use in a multiple initiator
environment.

SCSI-3 introduces persistent reserve/release, which does persist across
bus resets, but I know of no OS that implements it yet.

Furthermore, you'll often find that you have to turn reserve/release off
 to implement DDS.  This is because multiple hosts will have to access
the same SCSI device almost concurrently, by definition.

SCSI bus resets should be handled with zoning, and also should be
blocked at the SCSI/FC bridge, if possible.  Legato Bulletin 373
describes one of the ways in which spurious bus resets can occur.

You should also avoid running software that periodically probes the
hardware on hosts that share tape drives.  An example of this is HP-UX's
Event Monitoring Service.  These probes can cause tape drives to rewind
in the middle of a backup.

Saludos,
Jose.

References:

http://portal1.legato.com/resources/bulletins/373.html
http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x539393e260b0d611abdb0090277a778c,00.html

Carolina Garcia Santacruz wrote:
Aure,

Regarding the SCSI reserve release issue, you find it in the release notes
from 6.1 (and up), page 21:
"Bus Reset Can Rewind Tape on Devices Shared by Multiple Computers"

I think it is important that you read it and take it into consideration. You
are going to share your tape drive with at least another server, plus you
are carrying SCSI commands for your disks from the same HBA. One important
line there is that Microsoft does not support attaching any tape drive
to any shared SCSI bus that also hosts cluster-controlled disks.

Some tape devices (IBMs LTO at least) include this control and the rest are
planning on implementing it. SCSI 3 definition will include it. Some OS can
handle it --not MicroSoft AFAIK--. The patch I mentioned will prevent the
tapes from being overwritten, but does not work on the problem itself. I
don't see it as something that should stop you, but take some preventive
action.

Hope this helps,
Carolina

-----Original Message-----

From: Aurea Cruz [mailto:aurecruz AT YAHOO DOT COM]
Sent: 30. juni 2003 10:38
To: NETWORKER AT LISTMAIL.TEMPLE DOT EDU
Subject: Re: clustered storage nodes installation


<<...>>

I have been trying to find something about SCSI reserve  in Legato's
knowledge base but there doesn't seem to be much written. Is this really
still an issue? The admin guide on 6.1.x does not mention it, have not
checked in that for version 7. Should I stay out of it because of that? I
can't afford dedicating a drive to this cluster.


<<...>>

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