On Nov 27, 2007, at 4:32 PM, lemons_terry AT EMC DOT COM wrote:
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.
Thanks Terry;
In the meanwhile, does anyone have any home grown documentation (or
guidelines) on how to use udev for this purpose?
To sign off this list, send email to listserv AT listserv.temple DOT edu and type
"signoff networker" in the body of the email. Please write to networker-request
AT listserv.temple DOT edu if you have any problems with this list. You can access the
archives at http://listserv.temple.edu/archives/networker.html or
via RSS at http://listserv.temple.edu/cgi-bin/wa?RSS&L=NETWORKER
|
