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September 01, 2005

SVM / SDS numbering

SVM* (Solaris Volume Manager) is a pretty impressive bundle given that it comes free with Solaris. In fact it has almost** all the advantages of Veritas Volume Manager except for one small niggling issue - the device name / numbering limitation. You can only have 128 devices.

This sounds a lot but the traditional naming convention (d10 has children d11 and d12, d20 has children d21 and d22, ...) does not use the numbers very efficiently. You can work around this by using other schemes but the hassle is finding a scheme that is both obvious and easy - that way, tired sysadmins are less likely to make a mistake.

One alternative is to use parent/children combinations like: d30 -> d130, d230 (which reads as mirror d30 has a first submirror (d130) and a second submirror (d230)). The problem is the old 128 device limit.

Well it turns out that there is an easy fix for that. Grab your favourite editor (vi of course) and open up /kernel/drv/md.conf. Find the reference to nmd and change the value to something bigger (like 300). You now need to reboot your server....

Problem solved :-)

[* Formerly known as SDS (Sun Disk Suite).]
[** For a comparison, check out DiskSuite vs Volume Manager.]

Posted by Ozguru at September 1, 2005 06:00 AM