benefit of GEOM labels for ZFS, was Hard drive device names... serial numbers

[Graham Allan]

Sorry to come in late on this thread but I've been struggling with 
thinking about the same issue, from a different perspective.

Several months ago we created our first "large" ZFS storage system, 
using 42 drives plus a few SSDs in one of the oft-used Supermicro 
45-drive chassis. It has been working really nicely but has led to some 
puzzling over the best way to do some things when we build more.

We made our pool using geom drive labels. Ever since, I've been 
wondering if this really gives any advantage - at least for this type of 
system. If you need to replace a drive, you don't really know which 
enclosure slot any given da device is, and so our answer has been to dig 
around using sg3_utils commands wrapped in a bit of perl, to try and 
correlate the da device to the slot via the drive serial number.

At this point, having a geom label just seems like an extra bit of 
indirection to increase my confusion :-) Although setting the geom label 
to the drive serial number might be a serious improvement...

We're about to add a couple more of these shelves to the system, giving 
a total of 135 drives (although each shelf would be a separate pool), 
and given that they will be standard consumer grade drives, some 
frequency of replacement is a given.

Does anyone have any good tips on how to manage a large number of drives 
in a zfs pool like this?

Thanks,

Graham
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Graham Allan
School of Physics and Astronomy - University of Minnesota
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