redundant storage

[Steve O'Hara-Smith]

On Fri, 3 Jun 2016 12:14:46 +0200
Julien Cigar <julien.cigar at gmail.com> wrote:

> On Fri, Jun 03, 2016 at 10:41:38AM +0100, Steve O'Hara-Smith wrote:
> > 	Hi,
> > 
> > 	Just one change - don't use RAID1 use ZFS mirrors. ZFS does
> > better RAID than any hardware controller.
> 
> right.. I must admit that I haven't looked at ZFS yet (I'm still using
> UFS + gmirror), but it will be the opportunity to do so..!
> 
> Does ZFS play well with HAST?

	Never tried it but it should work well enough, ZFS sits on top of
geom providers so it should be possible to use the pool on the primary.

	One concern would be that since all reads come from local storage
the secondary machine never gets scrubbed and silent corruption never gets
detected on the secondary. A periodic (say weekly) switch over and scrub
takes care of this concern. Silent corruption is rare, but the bigger the
pool and the longer it's used the more likely it is to happen eventually,
detection and repair of this is one of ZFSs advantages over hardware RAID
so it's good not to defeat it.

	Drive failures on the primary will wind up causing both the primary
and the secondary to be rewritten when the drive is replaced - this could
probably be avoided by switching primaries and letting HAST deal with the
replacement.

	Another very minor issue would be that any corrective rewrites (for
detected corruption) will happen on both copies but that's harmless and
there really should be *very* few of these.

	One final concern, but it's HAST purely and not really ZFS. Writing
a large file flat out will likely saturate your LAN with half the capacity
going to copying the data for HAST. A private backend link between the two
boxes would be a good idea (or 10 gigabit ethernet).

> > On Fri, 3 Jun 2016 10:38:43 +0200
> > Julien Cigar <julien.cigar at gmail.com> wrote:
> > 
> > > Hello,
> > > 
> > > I'm looking for a low-cost redundant HA storage solution for our
> > > (small) team here (~30 people). It will be used to store files
> > > generated by some webapps, to provide a redundant dovecot (imap)
> > > server, etc.
> > > 
> > > For the hardware I have to go with HP (no choice), so I planned to buy
> > > 2 x HP ProLiant DL320e Gen8 v2 E3-1241v3 (768645-421) with 
> > > 4 x WD Hard Drive Re SATA 4TB 3.5in 6gb/s 7200rpm 64MB Buffer 
> > > (WD4000FYYZ) in a RAID1 config (the machine has a smartarray P222
> > > controller, which is apparently supported by the ciss driver)
> > > 
> > > On the FreeBSD side I plan to use HAST with CARP, and the volumes
> > > will be exported through NFS4.
> > > 
> > > Any comments on this setup (or other recommendations) ? :)
> > > 
> > > Thanks!
> > > Julien
> > > 
> > 
> > 
> > -- 
> > Steve O'Hara-Smith <steve at sohara.org>
> > 
> 


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