On Mar 21, 2011, at 5:32 AM, Edward Ned Harvey wrote: >> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- >> boun...@opensolaris.org] On Behalf Of Edward Ned Harvey >> >> it depends on the total number of used blocks that must >> be resilvered on the resilvering device, multiplied by the access time for >> the resilvering device. > > It is a safe assumption, if you've got a lot of devices in a vdev, that > you've probably got a lot of data in the vdev. And therefore the resilver > time for that vdev will be large.
Several studies have shown no correlation between the size of disks and the amount of data used. Or, to look at it another way, boot disks grow faster than OSes. > If you break your pool up into a bunch of mirrors, then the most data you'll > have in any one vdev is 1-disk worth of data. Fancy that, if you use raidz, the most data you will have to resilver is 1-disk worth of data. In the raidz case, the utilization of the resilvering disk is 100% and the utilization of the other disks is approximately (100% / N) > If you have a vdev whose usable capacity is M times a single disk, chances > are, the amount of data you have in the vdev is L times larger than the > amount of data you would have had in each vdev if you were using mirrors. > (I'm intentionally leaving the relationship between M and L vague, but both > are assumed to be > 1 and approaching the number of devices in the vdev > minus parity drives). Therefore the resilver time for that vdev will be > roughly L times the resilver time of a mirror. > For ZFS, usable capacity has no correlation to resilver time. -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
