Re: Intel SSD

On Tue, Feb 10, 2009 at 11:55 PM, John R Pierce <pierce@hogranch.com> wrote:
> Sebastian Böhm wrote:
>>
>> I consider buying one of these Intel SSDs for my Database (MLC).
>> .....
>> currently I have a lot of small random reads/writes causing heavy iowait.
>
> how many r/s and w/s in `iostat -x 5` while your database is humming are you
> seeing now?    Thats the single key performance factor in disk bound
> database IO.  Caches can reduce the r/s requirements but the writes have to
> go to disk if you want data integrity.   ok, a raid controller with battery
> back cache configured for writeback can accelerate the writes by a lot too.
>
> a desktop 7200 rpm SATA drive will saturate at under 100 IO ops/sec max with
> the typical 8kbyte random blocks of a database, while a 15k server drive can
> sustain 200 io/sec, and a raid 1+0 can hit several times more (I've seen
> sustained 200/s on each of 4 15k spindles) while still using normal hard
> disks.   Those intel SSDs are supposed to be good for 1000 or so IOP/sec if
> I remember correctly... (of course, in a mirror, you have to half the
> aggregated writes for the true number of useful random writes)

Also keep in mind that a fast battery backed caching RAID controller
can get several thousand transactions per second on a large number of
spindles by re-ordering writes and such.  I can get anywhere from 1800
to 3400 tps on 12 15k disks in RAID-10 (i.e. 6 disk RAID-0
performance) and that's sustained over a very long test, usually 30
minutes to a few hours with pgbench.  The size of the test set and
server config parameters make for the variations from 1800 to 3400.

I think the real advantage to the SSDs is that they can get this kind
of performance, or even more from a rather small software RAID-10 of 4
disks.  Instead of spending $800 on a RAID controller, use it towards
buying more SSDs.  As the price of SSDs falls much faster than the
cost of high end RAID controllers, they'll reach a point where any old
4x2.5" server can walk right into your data center and take over the
job of a much larger $10,000+ server.

I'd really like to see how 16 or more of them in a big RAID-10 both on
a RAID controller and maybe in jbod mode ran.  Anyone at some big
corporation got some time to benchmark the next great thing?  I'd take
a day off just to come watch that.