Hi Stan
If you use a FC driver level tool (like SANsurfer), you can create a persistent
binding between a WWNN/WWPN/Port ID on the SAN and a SCSI target on your host.
This form of persistent binding is not very interesting to backup applications
like NetWorker, which uses a higher-order construct (the device file, like
/dev/nst0) in its statically-defined resource definitions. So, even if the
target ID for a tape device doesn't change, the order in which device files are
assigned to tape devices can change, if another device is added to, for
instance, a FC bus that is scanned earlier in the system boot process.
Therefore, you want to use a persistent naming scheme for the device files that
NetWorker uses. Since you are using a Linux 2.6-based distribution, the
correct method of creating persistent names is with udev. A number of backup
administrators have begun writing their own udev rules to create persistent
names for their tape devices. These rules are fairly arcane, and take quite a
bit of study and tinkering. Plus, most of the rules that I've seen developed
are specific to the devices in each environment, right down to the serial
number of the tape drive. Thus, these rules are not flexible, and need to be
maintained.
It's an (apparently) little-known fact that SLES 9 and SLES 10 have udev rules
that automatically create persistently-named symbolic links for tape devices in
the /dev/tape/by-id directory. The next releases of RHEL 4 and RHEL 5 will
follow this convention, too. Using these persistently-named symbolic links
when configuring backup applications would allow a persistent path between the
backup application and the target device.
We should expect, and encourage, NetWorker and other backup applications to
evolve to use these persistent names.
tl
Terry Lemons
Backup Platforms Group
EMC²
where information lives
4400 Computer Drive, MS D239
Westboro MA 01580
Phone: 508 898 7312
Email: Lemons_Terry AT emc DOT com
-----Original Message-----
From: EMC NetWorker discussion [mailto:NETWORKER AT LISTSERV.TEMPLE DOT EDU] On
Behalf Of Stan Horwitz
Sent: Tuesday, November 27, 2007 11:19 AM
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Subject: [Networker] Persistent binding on Red Hat Enterprise Linux AS
(2.6.9-42.ELsmp)
I have a Qualstar tape library connected to a Linux box which is set
up as a NetWorker 7.4 Storage Node. This tape library has four LTO-3
drives. There is nothing fancy going on (i.e., no zoning or anything
like that). Each drive has its own fibre channel connection to the
Linux box, which is a Dell 9250. I can't see to get NetWorker to
remember the drive order so I assume I need to set up persistent
binding. The HBA cards are Dell branded Qlogic cards and I installed
the SANsurfer tool on it, but I don't see how to use it to set up
persistent binding and also how to consistently have the drives
numbered sequentially from bottom to top in nsrwatch or the NWCM. If
anyone knows, please let me know. Thanks.
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--
Stan Horwitz
Temple University
Enterprise Systems Group
stan AT temple DOT edu
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