redundant storage

[Valeri Galtsev]

On Fri, June 3, 2016 6:50 am, Julien Cigar wrote:
> On Fri, Jun 03, 2016 at 11:47:46AM +0100, Steve O'Hara-Smith wrote:
>> 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.
>
> Thanks, I'll read a bit on ZFS this week-end ..!
>
> My ultimate goal would be that the HAST storage survives an hard reboot/
> unplugged network cable/... during an heavy I/O write, and that the
> switch between the two nodes is transparent to the clients, without any
> data loss of course ... feasible or utopian? Needless to say that what
> I want to avoid at all cost is that the storage becomes corrupted and
> unrecoverable..!

Sounds pretty much like distributed file system solution. I tried one
(moosefs) which I gave up on, and after I asked (on this list) for advise
about other options, next candidate for me emerged: glusterfs, which I
hadn't chance to set up yet. You may want to search this list archives,
those were really good advises that experts gave me.

Valeri

>
>>
>> 	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).
>
> yep, that's what I had in mind..! one nic for the replication between
> the two HAST node, and one (CARP) nic by which clients access to
> storage..
>
>>
>> > > 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>
>> > >
>> >
>>
>>
>> --
>> Steve O'Hara-Smith                          |   Directable Mirror Arrays
>> C:>WIN                                      | A better way to focus the
>> sun
>> The computer obeys and wins.                |    licences available see
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>>
>
> --
> Julien Cigar
> Belgian Biodiversity Platform (http://www.biodiversity.be)
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>


++++++++++++++++++++++++++++++++++++++++
Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247
++++++++++++++++++++++++++++++++++++++++