Re: How to improve db performance with $7K? - Mailing list pgsql-performance

From Douglas J. Trainor
Subject Re: How to improve db performance with $7K?
Date
Msg-id cff304a11722a6d926cabb73e89b8919@transborder.net
Whole thread Raw
In response to Re: How to improve db performance with $7K?  (Alex Turner)
Responses Re: How to improve db performance with $7K?  ()
List pgsql-performance
You asked for it!  ;-)

If you want cheap, get SATA.  If you want fast under
*load* conditions, get SCSI.  Everything else at this
time is marketing hype, either intentional or learned.
Ignoring dollars, expect to see SCSI beat SATA by 40%.

     * * * What I tell you three times is true * * *

Also, compare the warranty you get with any SATA
drive with any SCSI drive.  Yes, you still have some
change leftover to buy more SATA drives when they
fail, but... it fundamentally comes down to some
actual implementation and not what is printed on
the cardboard box.  Disk systems are bound by the
rules of queueing theory.  You can hit the sales rep
over the head with your queueing theory book.

Ultra320 SCSI is king of the hill for high concurrency
databases.  If you're only streaming or serving files,
save some money and get a bunch of SATA drives.
But if you're reading/writing all over the disk, the
simple first-come-first-serve SATA heuristic will
hose your performance under load conditions.

Next year, they will *try* bring out some SATA cards
that improve on first-come-first-serve, but they ain't
here now.  There are a lot of rigged performance tests
out there...  Maybe by the time they fix the queueing
problems, serial Attached SCSI (a/k/a SAS) will be out.
Looks like Ultra320 is the end of the line for parallel
SCSI, as Ultra640 SCSI (a/k/a SPI-5) is dead in the
water.

Ultra320 SCSI.
Ultra320 SCSI.
Ultra320 SCSI.

Serial Attached SCSI.
Serial Attached SCSI.
Serial Attached SCSI.

For future trends, see:
http://www.incits.org/archive/2003/in031163/in031163.htm

    douglas

p.s. For extra credit, try comparing SATA and SCSI drives
when they're 90% full.

On Apr 6, 2005, at 8:32 PM, Alex Turner wrote:

> I guess I'm setting myself up here, and I'm really not being ignorant,
> but can someone explain exactly how is SCSI is supposed to better than
> SATA?
>
> Both systems use drives with platters.  Each drive can physically only
> read one thing at a time.
>
> SATA gives each drive it's own channel, but you have to share in SCSI.
>  A SATA controller typicaly can do 3Gb/sec (384MB/sec) per drive, but
> SCSI can only do 320MB/sec across the entire array.
>
> What am I missing here?
>
> Alex Turner
> netEconomist


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