On Thu, Sep 17, 2009 at 12:55:35PM +0200, Tomas Ögren wrote: > It's not a fixed value per technology, it depends on the number of disks > per group. RAID5/RAIDZ1 "loses" 1 disk worth to parity per group. > RAID6/RAIDZ" loses 2 disks. RAIDZ3 loses 3 disks. Raid1/mirror loses > half the disks. So in your 14 drive case, if you go for one big > raid6/raidz2 setup (which is larger than recommended for performance
I presume for 24 disks (my next project, the current 16-disk one had to be converted to CentOS for software compatibility reasons) you would recommend splitting them into two groups, a la 12 disks. With raidz3, there would be 9 disks left for data, 18 total -- 36 TBytes effective in case of 2 TByte WD RE4 drives, half that for WD Caviar Black. How many hot spares should I leave in each pool, one or more? Is it safe to stripe over two such 12-disk pools? Or is mirror the right thing to do, regardless of drive costs? Speaking of which, does anyone use NFSv4 clustering in production to aggregate individual zfs boxes? Experiences good/bad? > reasons), you will lose 2 disks worth of storage to parity leaving 12 > disks worth of data. With raid10 you will lose half, 7 disks to > parity/redundancy. With two raidz2 sets, you will get (5+2)+(5+2), that > is 5+5 disks worth of storage and 2+2 disks worth of redundancy. The > actual redudancy/parity is spread over all disks, not like raid3 which > has a dedicated parity disk. So raidz3 has a dedicated parity disk? I couldn't see that from skimming http://blogs.sun.com/ahl/entry/triple_parity_raid_z > For more info, see for example http://en.wikipedia.org/wiki/RAID Unfortunately, this is very thin on zfs. http://www.solarisinternals.com/wiki/index.php/ZFS_Best_Practices_Guide is very helpful, but it doesn't offer concrete layout examples for odd number of disks (understandable, since Sun has to sell the Thumper), and is pretty mum on raidz3. Thank you. This list is fun, and helpful. -- Eugen* Leitl <a href="http://leitl.org";>leitl</a> http://leitl.org ______________________________________________________________ ICBM: 48.07100, 11.36820 http://www.ativel.com http://postbiota.org 8B29F6BE: 099D 78BA 2FD3 B014 B08A 7779 75B0 2443 8B29 F6BE _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
