On 11 Nov, 2014 3:11 PM, "Adam Leventhal" <[email protected]> wrote: > > Hey Andrew, > > Having a raidz3 vdev with two missing devices is significantly worse > than raidz1. The computational costs would be far far higher. With > raidz1 reading requires no reconstruction (and even then, raidz1 > reconstruction is just xor). The raidz3 configuration you're > describing would require expensive, 2-column reconstruction most of > the time, and with a far more expensive mechanism than the simple xor > of raidz1, doing calculations over a Galois field. For details: > > https://github.com/illumos/illumos-gate/blob/b515258426fed6c7311fd3f1dea697cfbd4085c6/usr/src/uts/common/fs/zfs/vdev_raidz.c#L937 > > Adam > > ... and if this is someone from the ZFS developer summit trolling me, > well done! ;-) > >
No... I wish it was though... Thanks for the explain... Back to sleep... > > On Mon, Nov 10, 2014 at 6:24 PM, Andrew Barnes <[email protected]> wrote: > > Hi All, > > > > Hope you are all doing well, well done on the summit I have been keeping my > > eye on the stream, many thanks. > > > > I've had a thought in the back of my head for a while... I assume this has > > been asked before so apologies in advance. > > > > Is there any downside to a raidz3 with 2 missing devices v's a raidz1? > > > > If not, would it be viable to make ZFS always create raidz3's in the > > background even if you ask for a raidz1 or a raidz2 and internally take into > > account the raid level and adjust status reporting appropriately to allow > > reshaping between the 3 levels? > > > > Many thanks, > > > > Andrew > > > > _______________________________________________ > > developer mailing list > > [email protected] > > http://lists.open-zfs.org/mailman/listinfo/developer > > > > > > -- > Adam Leventhal > CTO, Delphix > http://blog.delphix.com/ahl
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