Comments for Miscellaneous Ramblings http://www.miscellaneous.net Wed, 07 Jan 2009 04:00:36 +0000 http://wordpress.org/?v=2.7 hourly 1 Comment on Fighting with SAN by John Scott http://www.miscellaneous.net/2008/12/23/fighting-with-san/comment-page-1/#comment-2 John Scott Tue, 23 Dec 2008 18:22:21 +0000 http://www.miscellaneous.net/?p=171#comment-2 From my prior e-mail - (Thanks for enabling comments!) 1) Qlogic HBAs make it easy to see one path (if you do not desire to do load balancing and you aren’t using EMC powerpath). The ql2xfailover=1 kernel flag given to the qla2xxx module in modprobe.conf provides failover functionality and allows you to see a single device instead of seeing multiples for each LUN. For Linux boxes, I always like Qlogic HBAs regardless of whether I’m using EMC powerpath or not. If you’re using PowerPath, PowerPath will takes care of both making device names that do not change (/dev/emcpower[abc][123]) and takes care of load balancing and failover. EMC recommends against using ql2xfailover=1 for this reason. Powerpath is annoying, however, particularly if you want to use an /dev/emcpowerX1 device as a boot device. 2) I’ve had similar issues to yours with shrinking LUNs. Better to start small. It’s simple to grow a filesystem but shrinking is nasty. 3) Labeling your partitions is a great way to find them again and mount them in the right place, however, if you get a wild hair, just tweak udev to create symlinks for the devices you want to use so that they are always there and always in the right order. A good article about that: http://www.cyberciti.biz/tips/linux-assign-static-names-to-scsi-devices.html This was a good post. Keep them coming! Sysadminery lives at miscellaneous.net! Your friend, -John From my prior e-mail - (Thanks for enabling comments!)

1) Qlogic HBAs make it easy to see one path (if you do not desire to do load balancing and you aren’t using EMC powerpath). The ql2xfailover=1 kernel flag given to the qla2xxx module in modprobe.conf provides failover functionality and allows you to see a single device instead of seeing multiples for each LUN. For Linux boxes, I always like Qlogic HBAs regardless of whether I’m using EMC powerpath or not. If you’re using PowerPath, PowerPath will takes care of both making device names that do not change (/dev/emcpower[abc][123]) and takes care of load balancing and failover. EMC recommends against using ql2xfailover=1 for this reason. Powerpath is annoying, however, particularly if you want to use an /dev/emcpowerX1 device as a boot device.

2) I’ve had similar issues to yours with shrinking LUNs. Better to start small. It’s simple to grow a filesystem but shrinking is nasty.

3) Labeling your partitions is a great way to find them again and mount them in the right place, however, if you get a wild hair, just tweak udev to create symlinks for the devices you want to use so that they are always there and always in the right order. A good article about that:

http://www.cyberciti.biz/tips/linux-assign-static-names-to-scsi-devices.html

This was a good post. Keep them coming! Sysadminery lives at miscellaneous.net!

Your friend,
-John

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