On Thu, Jul 23, 2009 at 12:29 PM, thomas<no-re...@opensolaris.org> wrote: > Hmm.. I guess that's what I've heard as well. > > I do run compression and believe a lot of others would as well. So then, it > seems > to me that if I have guests that run a filesystem formatted with 4k blocks for > example.. I'm inevitably going to have this overlap when using ZFS network > storage? > > So if "A" were zfs blocks and "B" were virtualized guest blocks, I think it > might > look like this with compression on? > > | B1 | B2 | B3 | B4 | > | A1 | A2 | A3 | A4 | > > So if the guest OS wants blocks B2 or B4, it actually has to read 2 blocks > from the > underlying zfs storage?
AFAIK If you use zvol, and set zfs volblocksize to be the same as the fs block size on virtualized system (which is 4k by default for several GB disk/partition with ext3/ntfs), every virtualized block read should correspond to one zfs block read. If you set compression on, the actual bytes read from the storage will not always be 4k though, it can be less depending on how compressible the data is. -- Fajar _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
