On Wed, Sep 17, 2008 at 10:11 AM, gm_sjo <[EMAIL PROTECTED]> wrote: > 2008/9/17 Peter Tribble: >> On Wed, Sep 17, 2008 at 8:40 AM, gm_sjo <[EMAIL PROTECTED]> wrote: >>> Am I right in thinking though that for every raidz1/2 vdev, you're >>> effectively losing the storage of one/two disks in that vdev? >> >> Well yeah - you've got to have some allowance for redundancy. > > This is what i'm struggling to get my head around - the chances of > losing two disks at the same time are pretty darn remote (within a > reasonable time-to-replace delta), so what advantage is there (other > than potentially pointless uber-redundancy) in running multiple > raidz/2 vdevs? Are you not infact losing performance by reducing the > amount of spindles used for a given pool?
No. The number of spindles is constant. The snag is that for random reads, the performance of a raidz1/2 vdev is essentially that of a single disk. (The writes are fast because they're always full-stripe; but so are the reads.) So your effective random read performance is that of a single disk times the number of raidz vdevs. It's a tradeoff, as in all things. Fewer vdevs means less wasted space, but lower performance. -- -Peter Tribble http://www.petertribble.co.uk/ - http://ptribble.blogspot.com/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
