On Sun, Jan 08, 2012 at 06:59:57AM +0400, Jim Klimov wrote: > 2012-01-08 5:37, Richard Elling ??????????: >> The big question is whether they are worth the effort. Spares solve a >> serviceability >> problem and only impact availability in an indirect manner. For single-parity >> solutions, spares can make a big difference in MTTDL, but have almost no >> impact >> on MTTDL for double-parity solutions (eg. raidz2). > > Well, regarding this part: in the presentation linked in my OP, > the IBM presenter suggests that for a 6-disk raid10 (3 mirrors) > with one spare drive, overall a 7-disk set, there are such > options for "critical" hits to data redundancy when one of > drives dies: > > 1) Traditional RAID - one full disk is a mirror of another > full disk; 100% of a disk's size is "critical" and has to > be prelicated into a spare drive ASAP; > > 2) Declustered RAID - all 7 disks are used for 2 unique data > blocks from "original" setup and one spare block (I am not > sure I described it well in words, his diagram shows it > better); if a single disk dies, only 1/7 worth of disk > size is critical (not redundant) and can be fixed faster. > > For their typical 47-disk sets of RAID-7-like redundancy, > under 1% of data becomes critical when 3 disks die at once, > which is (deemed) unlikely as is. > > Apparently, in the GPFS layout, MTTDL is much higher than > in raid10+spare with all other stats being similar. > > I am not sure I'm ready (or qualified) to sit down and present > the math right now - I just heard some ideas that I considered > worth sharing and discussing ;) >
Thanks for the video link (http://www.youtube.com/watch?v=2g5rx4gP6yU). It's very interesting! GPFS Native RAID seems to be more advanced than current ZFS, and it even has rebalancing implemented (the infamous missing zfs bp-rewrite). It'd definitely be interesting to have something like this implemented in ZFS. -- Pasi _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
