> From: Brandon High [mailto:bh...@freaks.com] > > On Wed, May 4, 2011 at 8:23 PM, Edward Ned Harvey > <opensolarisisdeadlongliveopensola...@nedharvey.com> wrote: > > Generally speaking, dedup doesn't work on VM images. (Same is true for > ZFS > > or netapp or anything else.) Because the VM images are all going to have > > their own filesystems internally with whatever blocksize is relevant to the > > guest OS. If the virtual blocks in the VM don't align with the ZFS (or > > whatever FS) host blocks... Then even when you write duplicated data > inside > > the guest, the host won't see it as a duplicated block. > > A zvol with 4k blocks should give you decent results with Windows > guests. Recent versions use 4k alignment by default and 4k blocks, so > there should be lots of duplicates for a base OS image.
I agree with everything Brandon said. The one thing I would add is: The "correct" recordsize for each guest machine would depend on the filesystem that the guest machine is using. Without knowing a specific filesystem on a specific guest OS, the 4k recordsize sounds like a reasonable general-purpose setting. But if you know more details of the guest, you could hopefully use a larger recordsize and therefore consume less ram on the host. If you have to use the 4k recordsize, it is likely to consume 32x more memory than the default 128k recordsize of ZFS. At this rate, it becomes increasingly difficult to get a justification to enable the dedup. But it's certainly possible. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
