I''m being a bit of a dunderhead at the moment and neither the site search nor google are picking up the information I seek... I''m setting up a thumper and I''m sure I recall some discussion of the optimal number of drives in raidz1 and raidz2 vdevs. I also recall that it was something like you would want an even number of disk for raidz1, and an odd number for raidz2 (so you always have an odd number of data drives). Have I remembered this correctly, or am I going delusional? And, if it is the case, what is the reasoning behind it? Thanks, -- -Peter Tribble http://www.petertribble.co.uk/ - http://ptribble.blogspot.com/ -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.opensolaris.org/pipermail/zfs-discuss/attachments/20070104/f5c41d71/attachment.html>
Hey Peter, If I recall correctly, the result was there was a very slight space-efficiency benefit of using a multiple of 2 vdevs for raidz1 and of 3 vdevs for raidz2 -- doing this can reduce the number of ''skipped'' blocks. That said, the advantage is very slight and is only really relevant when the blocksize or recordsize is relatively closer to the number of bytes in a stripe. Adam On Thu, Jan 04, 2007 at 11:17:26PM +0000, Peter Tribble wrote:> I''m being a bit of a dunderhead at the moment and neither the site search > nor > google are picking up the information I seek... > > I''m setting up a thumper and I''m sure I recall some discussion of the > optimal > number of drives in raidz1 and raidz2 vdevs. I also recall that it was > something > like you would want an even number of disk for raidz1, and an odd number for > raidz2 (so you always have an odd number of data drives). Have I remembered > this correctly, or am I going delusional? And, if it is the case, what is > the > reasoning behind it? > > Thanks, > > -- > -Peter Tribble > http://www.petertribble.co.uk/ - http://ptribble.blogspot.com/> _______________________________________________ > zfs-discuss mailing list > zfs-discuss at opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss-- Adam Leventhal, Solaris Kernel Development http://blogs.sun.com/ahl
Hi Peter, Peter Tribble wrote:> I''m being a bit of a dunderhead at the moment and neither the site > search nor google are picking up the information I seek...There was the thread named "Metaslab alignment on RAID-Z" on this list, you may want to look at it.> > I''m setting up a thumper and I''m sure I recall some discussion of the > optimal number of drives in raidz1 and raidz2 vdevs. I also recall > that it was something like you would want an even number of disk for > raidz1, and an odd number for raidz2 (so you always have an odd > number of data drives). Have I remembered this correctly, or am I > going delusional? And, if it is the case, what is the reasoning > behind it?In short is is better to have * power of 2 plus 1 more disk for RAID-Z * power of 2 plus 2 more disks for RAID-Z2 this way you will always have even (power of 2) number of data disks. With general recommendation of one-digit number of disks in vdev, this leaves you basicly with these options: 3,5 or 9 disks for RAID-Z vdev 4,6 or 10 disks for RAID-Z2 vdev Hth, Victor