Re: how can we help DSA save money
On Mon, Jul 22, 2013 at 07:13:57PM +0200, Tollef Fog Heen wrote:
> ]] Steven Chamberlain
>
> > On 2013-07-22 15:49, Tollef Fog Heen wrote:
> > > It's not, it's a limitation of resizing a raid and that requiring about
> > > a billion seeks across the disk surface.
> >
> > I didn't realise it was hardware RAID.
> >
Anything large-ish is going to be hardware raid. Most people (apparently) regard
16TB as large - Red Hat conference this year - and very few people have
single filesystems that are larger (allegedly).
> > If for example it is possible to create multiple, smaller hardware RAIDs
> > over time, then maybe all that is needed is a small code change to
> > snapshot.d.o to spread files across multiple mountpoints, which would
> > surely be worth it.
>
Mirroring all of Debian is really really tough. There's a huge amount of data.
> I don't think the extra complexity that would entail would be worth it,
> and it's anyway moot until that code shows up. The current snapshot
> hosting is just about full.
>
> > But it seems to me that software RAID, probably running free Debian
> > software, can someday reduce need of some hardware, if it were reliable,
> > performed well and could be managed easily. (It seems DSA are now doing
> > this for compute resources, through OpenStack and ganeti).
>
> (We're not yet doing it with openstack, we've talked about doing it,
> though.)
>
> Running software raid on disks on a SAN is asking for trouble as well as
> poor performance. Your disks are at the end of a network and
> multiplying the number of requests going over that network is a recipe
> for poor performance.
>
+400 - this is _so_ right :)
> > I just like the idea that Debian can strive to develop such things for
> > its own infrastructure needs. I think storage makes for a good
> > long-term project, but there may be others that could yield higher savings.
>
> I'd love to have good and free SAN solutions that one could buy and get
> warranties for replacement parts on. Sadly, we're not there today, and
> I'm not aware of anything obvious on the horizon either.
>
HP / IBM / (possibly Dell) or, if you really want to push the boat out, NetApp.
It's all hardware raid, enterprise priced disks, sitting in cooled data centre
air. NetApp is complex and proprietary behind the scenes to produce simplicity
for the end user. I did consider doing some of this for myself with 10 3TB drives
in a tower case but you _still_ need highest quality hardware RAID. If 3TB is ~£150,
I'd expect to pay £450 for something that will handle 12 cheap SATA drives so £2000
for 24TB RAID 6. An expensive tower case,PSU and something like an AMD 4 core == £400.
Approximately £2400 overall for 24TB
That's about the same as 2 x 2TB enterprise class drives / half an (old)
IBM disk shelf to hold them.
You could save the cost of the RAID card and bring it down to below £2000
BUT - BUT - BUT
Software RAID on > 16TB and you're dicing with death, in my opinion.
Just my 0.02€
Andy
> --
> Tollef Fog Heen
> UNIX is user friendly, it's just picky about who its friends are
>
>
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