news.tele.dk wrote:



I wouldn't recommend using SATA drives for online transactions, assuming
that's what you intend.
Using SCSI drives is what I would recommend for I/O intensive
applications.


SATA was chosen based on cost/benefit.
We figured we could buy approx. 4 times the amount of SATA disks
compared to SCSI.

Some of Tom's hardware recent tests was very promissing abount SATA
compared to SCSI...

All else being equal, SATA single drives seem to come pretty close to the
performance level of SCSI drives. But a high-end SATA drive is an
entry-level SCSI drive. Maybe that will change eventually. Right now SATA
has a way to go before it becomes a viable substitute even for PATA, let
alone SCSI.

What is your target bandwidth? Also, are you sure high bandwidth is what
you need? To me it sounds like you're going to need IOPS (I/O per
second). I'm not sure what specific SQL engine you'll be using, but
generally SQL uses an I/O size of 2-8 kB for online transactions. Data
warehouse is another matter.

We don't have a target bandwidth, the system is bought to host a rather
new product, and the load right now is rather low.
The server can actually easy handle the current load, but when it first is
set in production (at an external hosting partner),
you know how hard it is to upgrade, so we would like it to last as long as
possible = maximize the current configuration.

So we could live with the current configuration... but if we could get the
same I/O speed for less money, why buy the
top-of-the-line-adaptec-sata-card ??? money out the window I say.

Whoever told you that Adaptec was "top of the line" is an idiot. Adaptec
RAID controllers have never worked particularly well and their ATA RAID
controllers even less so. See what IBM uses in their servers--you'll find
that it's Mylex, which IBM spun off to LSI Logic a while back. LSI Logic
has a nice family of SATA RAID controllers that might be worth a look. You
could also look at 3Ware, which specializes in SATA RAID. Since you're
using an Intel server board, an Intel RAID controller (designs are similar
but not identical to LSI IIRC) might be another viable option.

What you're going to have to do though is try the various boards in your
server until you find one that hits your performance objectives or have
gone through all of them.

Further more, we expect to buy two machines and have the partitions of the
server (linux) be mirrored
via http://www.drbd.org/ (via a crossed GLAN cable), so a bad IO card is
actually two :-)

I don't have any figures on-hand what kind of I/O rate a single SATA
drive can do while keeping a reasonable response time (20 ms being the
maximum value I've learned) but considering the drive's specs are 7,2
krpm and average seek 9.3 ms (taken from the data sheet of a Maxtor
DiamondMax Plus 9) I don't expect this drive to be able to handle more
than maybe 100-120 IOPS in a random r/w I/O pattern. Let's for arguments
sake say it can deliver up to 200 IOPS, and each I/O is 8kB. The total
bandwidth would then be 200*8*12 (12 is the number of drives in your
setup) = 19.2 MB/s. This is of course not factoring in RAID overhead.

That's why we bought the server with a fair amount of RAM, we should be
able to have the
currently active database objects in RAM, and a fair speed when seeking in
the "archives" (which is actually also your later stated point)

The battery option should take care of I/O writes.

Huh? The only thing the battery option does is hold the data in the cache
in the event of a power outage until the power is restored. It has nothing
whatsoever to do with performance.

AAAAArrhhhggggggggg money out the window....

Possibly, but it might depend on what you consider "massive SQL-database
transactions". Then again, in my experience many on-line SQL systems I've
delivered the disk subsystem to hardly uses any disk resources during
normal operation. Most transactions are handled in RAM, and never see the
disks. RAM being so cheap today, it makes good sense cramming as much
memory into the host and not worry about the disk subsystem. Perhaps this
is what you'll see too.

I've examined benchmarks on other cards posted on the net, unfortunaly no
one
has tested the 21610SA against other cards (I wonder why?)

We should be able to get at least 400-600 mb/sec bandwidth to the disk
system.

I can see that our server-supplier also sells 3Ware, we will try to buy
the 12
port SATA (9500) card next week, I wonder why they didn't mentioned all
this to us when we bought the system.

If I get the time I'll maybe post the tests.

mvh,
Carsten

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)