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Re: PostgreSQL data on a NAS device ?

From: Will LaShell <will(at)lashell(dot)net>
To: Alexander Priem <ap(at)cict(dot)nl>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: PostgreSQL data on a NAS device ?
Date: 2003-10-20 15:29:32
Message-ID: 1066663774.26155.25.camel@lyric.ofsloans.com (view raw or flat)
Thread:
Lists: pgsql-performance
Hello Alexander,

On Mon, 2003-10-20 at 06:04, Alexander Priem wrote:
> Even better than the four-disk NAS I mentioned earlier is the following:
> 
> Promise UltraTrak RM8000. This is a so-called SCSI-to-IDE RAID system.
> Basically it's a RAID setup of eight IDE disks, using a hardware RAID
> engine, that's connected to (in this case) the PostgreSQL server via a SCSI
> Ultra160 interface (!). So the server won't know any better than that
> there's a SCSI disk attached, but in reality it's a IDE RAID setup. It
> supports RAID levels 0, 1, 0+1, 5, 50 and JBOD and supports hot-swapping.

We have a Promise FasTrak 4000 in our development server connected to
120 Gig western digital 8mb cache drives. Basically the fastest drives
we could get for an ide configuration. This system works well, however
there are a few things you need to consider.  The biggest is that you
have very limited control over your devices with the Promise
controllers. The bios of the raid controller doesn't have many options
on it. You basically plug everything together, and just hope it works.

It usually does, but there have been times in the past that really gave
us a scare. And we had a situation that in a hard poweroff ( UPS died )
we suffered complete corruptions of 2 of our 4 drives. 

Performance wise it is =okay= but definitely not on par with either our
Megaraid elite 1650 controller or a solution I'm going to suggest to you
later in this mail. Your biggest hit is going to be multiple
simultaneous accesses. The controller and drives just can't keep up to
it.

Realistically with my experiences I cannot recommend this solution for a
production machine, even with the budget constraints you have put forth.

> 
> Such a NAS config would cost around EUR 3700 (ex. VAT), using 8x40 Gb IDE
> disks (7200rpm).
> 
> A SCSI RAID-10 setup using 6x18Gb (15000rpm) disks would cost around EUR
> 6000 (ex. VAT) so it's a big difference...

I'm not sure where you have your figures, but I would like to propose
the following solution for you.

for your boot device use either a single ide drive and keep an exact
duplicate of the drive in the event of a drive failure, or use 2 drives
and use software raid to mirror the two.  In this manner you can spend
approx  $100 USD for each drive and no additional cost for your
controller as you will use the motherboards IDE controller.

For your postgresql partition or even /var use software raid on an
adaptec 29320-R SCSI controller. (
http://www.adaptec.com/worldwide/product/proddetail.html?sess=no&language=English+US&prodkey=ASC-39320-R&cat=%2fTechnology%2fSCSI%2fUltra320+SCSI )  cost: $399 USD  IF you bought it from adaptec

Match this with 6 Seagate 10k 36G Cheetah U320 scsi drives: 
( http://www.c-source.com/csource/newsite/ttechnote.asp?part_no=207024 )
for a cost of $189 USD per drive.  If you have 6 of them  it brings the
total price for your drives to $1134 USD.

Total cost for this would be approx $1633 before shipping costs. We use
this configuration in our two file servers and have nothing but positive
results.  If you are totally unable to use software raid you could still
buy 6 of those drives, and spend approx $900 USD on an LSI Megaraid 1650
controller.

I really believe you'll find either of those options to be superior in
terms of price for you.

Sincerely,

Will LaShell


 
> Does anyone have experience with this NAS device or other "SCSI-to-IDE" RAID
> systems? Are they OK in terms of performance and reliability?

> Kind regards,
> Alexander.
> 
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 7: don't forget to increase your free space map settings

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