>>>>> "mb" == Mike Brancato <[EMAIL PROTECTED]> writes:
mb> if a 4x100GB raidz only used 150GB of space, one could do
mb> 'zpool remove tank c0t3d0' and data residing on c0t3d0 would
mb> be migrated to other disks in the raidz.
that sounds like in-place changing of stripe width, and wasn't part of
the discussion I remember. We were wishing for vdev removal, but
you'd have to remove a whole vdev at a time. It would be analagous to
'zpool add', so just as you can't add 1 disk to widen a 3-disk raidz
vdev to 4-disks, you couldn't do the reverse even with the wished-for
feature.
To change from 4x100GB raidz to 3x100GB raidz, you'd have to:
zpool add pool raidz disk5 disk6 disk7
zpool evacuate pool raidz disk1 disk2 disk3 disk4
RFE 4852783 is to create something like zpool evacuate, removing the
whole vdev at once and migrating onto other vdev's, not other disks.
The feature's advantage as-is would be for pools with many vdev's. It
could also be an advantage for pools with just one vdev that are
humongous: you want to change the shape of the 1 vdev, but you need to
do the copy/evacuation online because it takes a week. If not for the
week, on a 1-vdev pool you could destroy the pool and make a new one
without needing any more media than you would with the new feature.
For home storage with big, slow, cheap pools, what you want sounds
nice. Someone once told me he'd gotten Veritas to change a plex's
width with the vg online, but for me I think it's scary because, if it
crashed halfway through, I'm not sure how the system could communicate
to me what's happening in a way I'd understand, much less recover from
it. I'm not saying Veritas doesn't do both, just that I'd chuckle
happily if I saw it actually work (which was the storyteller's
response too). For vdev removal I think you could harmlessly stop the
evacuation at any time with only O(1) quickie-import-time recovery,
without needing to communicate anything. much easier. so i like the
RFE as-is, analagous to Linux LVM2's pvmove.
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