scu utility to disable scsi reserve

[Cecelia Brandenstein]

We are having a problem using Legato's Networker in our environment. We have a tape
library, fibre attached to a san. We have
many Tru64 nodes set up as Networker clients.
We have a Solaris server as our Networker server.

When we start backups on one Tru64 node and do
any type of san work or even type an mt status
command on a separate node, the backup aborts
on an io error.

In the Networker admin guide, it says that we
have to "disable the scsi reserve/release"
through the scu utility.

Does anyone know how to do that? We can not
see this option when we issue the scu command.

Has anyone ever seen this happening in their
environment? If so, did you use the scu
utility to correct it?

[Johan Brusche]

You do not mention the Tru64 version, but V4.0G till V5.1B certainly have a "scu release" command

/sbin/scu

scu> sbtl b# t# l#
scu> release device


__ Johan.

[Eric van Dijken]

(yes, i know its bad practice to ask a question in somebody elses thread)

@Johan
Wouldn't that just release the device one time only? I think, what the Legato manual means is that you have to disable the persitent reserve. Not just to release the currently claimed device.

[Han Pilmeyer]

There are different kinds of reservations.

In TruCluster V4 environment, SCSI reserves were used as an I/O barrier. Those could be cleared by doing a device reset.

In TruCluster Server V5 environment, persistent group reservations (PGR) SCSI-3 commands are use to persistently reserve a device. scu can be used to release those, although the easier command to do this would be "cleanPR".

In V5.1B a new feature was introduced to reserve tape drives for applications. Looks at the commands "release" and "reserve" for the "mt" utility. This could be wat Legato is referring to.

Note that inadvertently clearing any of the above reservations can lead to data corruption. Use extreme caution!

[Cecelia Brandenstein]

Thanks to everyone who responded. This
information is all new to me. Especially
the part where a unix command entered on
one node could abort the backup running
on another.

The version of Tru64 is 5.1b pk3 with a
customized patch for Networker. Sorry I
didn't mention it in the original email.

I too was under the impression that what
was written in the Networker Admin guide
had to do with disabling the reserve at the
os level. If I use the release command
either with the mt or scu, will the release
disable the os from placing any more reserves
on the tape drive or will the release just
affect the current operation?

[Han Pilmeyer]

IF we're talking about the reserve/release done by the "mt" command, then Legato is supposed to do that.

[Eric van Dijken]

We use Legato (7.1.2) on our Tru64 Cluster(5.1b/PK4 with the cam_scsi ERP HP patches (3 of them)) on SAN attached SDLT drives.

And don't use any scsi reserve/release command on the OS level. And everything works without problems.

[Cecelia Brandenstein]

We are planning an upgrade to patchkit 4. I
will ask the admins to verify that the cam
patches were also applied.

Han - if Networker is supposed to use the mt
command to do the reserve/release, does this
mean that if someone, independent of
Networker, were to issue an mt status
command, would they/should they receive a
busy status ?

One of the issues that started this search
was this event. If placing a reserve on the
drive with the mt command should prevent
others from accessing the drive, then maybe
Legato is not using the mt command.

I do have an open support ticket with Legato
who claim they have never heard of such a
thing happening with os commands.

[Han Pilmeyer]

Legato wouldn't be using the "mt" command. There is also an API using some ioctl(). Legato was supposed to start using this API with version 7.

The tape reserve will actually also put a SCSI reserve on the tape drive. The "mt" command can be used to clear that reserve. This should NOT be done through the "scu" command.

Before using the "mt reserve" command, the "scu tur" command should be used to determine whether the tape is free for use.

I wouldn't know what Legato is referring to with the "disable the scsi reserve/release through the scu utility" statement. If you give a pointer to the document, then I can try to look into it.

[Cecelia Brandenstein]

The reference to the scu utility can be found
in the Networker admin guide for Unix version
7.1.1 on page 257 under device and media
management. I believe that other versions also have this reference.

This guide can be found on Legato's web-site
at this link --
http://web1.legato.com/cgi-bin/catalog?sf=Releases&level=17-5#17-5

Thanks for all your help

[Han Pilmeyer]

This statement from Legato makes absolutely no sense at all to the people who developed this functionality. Which means we will have to take this up with Legato...