Re: SAN performance mystery

On 6/16/06, Mikael Carneholm <Mikael(dot)Carneholm(at)wirelesscar(dot)com> wrote:
> We've seen similar results with our EMC CX200 (fully equipped) when
> compared to a single (1) SCSI disk machine. For sequential reads/writes
> (import, export, updates on 5-10 30M+ row tables), performance is
> downright awful. A big DB update took 5-6h in pre-prod (single SCSI),
> and 10-14?h (don't recall the exact details) in production (EMC SAN).
> And this was with a proprietary DB, btw - no fsync on/off affecting the
> results here.

You are in good company. We bought a Hitachi AMS200, 2gb FC and a
gigabyte of cache. We were shocked and dismayed to find the unit
could do about 50 mb/sec measured from dd (yes, around the performance
of a single consumer grade sata drive). It is my (unconfirmted)
belief that the unit was governed internally to encourage you to buy
the more expensive version, AMS500, etc.

needless to say, we sent the unit back, and are now waiting on a
xyratex 4gb FC attached SAS unit. we spoke directly to their
performance people who told us to expect the unit to be network
bandwitdh bottlenecked as you would expect. they were even talking
about a special mode where you could bond the dual fc ports, now
that's power. If the unit really does what they claim, I will be back
here talking about it for sure ;)

The bottom line is that most SANs, even from some of the biggest
vendors, are simply worthless from a performance angle. You have to
be really critical when you buy them, don't beleive anything the sales
rep tells you, and make sure to negotiate in advance a return policy
if the unit does not perform. There is tons of b.s. out there, but so
far my impression of xyratex is really favorable (fingers crossed),
and I'm hearing lots of great stuff about them from the channel.

merlin