Re: advice on raid controller - Mailing list pgsql-performance

On 29 Sep 2003, Will LaShell wrote:

> On Mon, 2003-09-29 at 06:48, scott.marlowe wrote:
> > I've used the megaraid / LSI cards in the past and they were pretty good
> > in terms of reliability, but the last one I used was the 328 model, from 4
> > years ago or so.  that one had a battery backup option for the cache, and
> > could go to 128 Meg.  We tested it with 4/16 and 128 meg ram, and it was
> > about the same with each, but we didn't do heavy parallel testing either.
> >
> > Here's the page on the megaraid cards at lsilogic.com:
> >
> > http://www.lsilogic.com/products/stor_prod/raid/ultra320products.html
> >
> > On Sun, 28 Sep 2003, Matt Clark wrote:
> >
> > > As others have mentioned, you really ought to get battery-backed cache if
> > > you're doing any volume of writes.  The ability to do safe write-back
> > > caching makes an *insane* difference to write performance.
> > >
> > > The site you link to also has that for only 15% more money:
> > > http://uk.azzurri.com/product/product.cgi?productId=80
> > >
> > > No experience with the card(s) I'm afraid.
> > >
> > > In general though, U320 will only be faster than U160 for large sequential
> > > reads, or when you have silly numbers of disks on a channel (i.e. more than
> > > 4/channel).  If you have silly numbers of disks, then RAID5 will probably be
> > > better, if you have 4 disks total then RAID1+0 will probably be better.  In
> > > between it depends on all sorts of other factors.  Bear in mind though that
> > > if you *do* have silly numbers of disks then more channels and more cache
> > > will count for more than anything else, so spend the money on that rather
> > > than latest-and-greatest performance for a single channel.
>
> Just to add my thoughts,  we use the MegaRaid Elite 1650 in 3 servers
> here that drive our core databases.  We paired up the controllers with
> the Seagate Cheetah 10k drives,  we could have purchased the X15's which
> are Seagate's 15k version, but due to budget constraints and lack of
> true performance increase from the 10k to the 15k rpm drives we didn't
> opt for them.
>
> I have to say that I've been 100% pleased with the performance and
> reliability of the Megaraid controllers. They do everything a good
> controller should and they are very easy to manage. The driver is
> actively maintained by the guys at LSI and their tech support personnel
> are very good as well.
>
> If you want any specific information or have any questions about our
> experience or configuration please feel free to contact me.

To add one more feature the LSI/MegaRAIDs have that I find interesting,
you can put two in a machine, build a RAID0 or 5 on each card, then mirror
the two cards together, and should one card / RAID0 ot 5 chain die, the
other card will keep working.  I.e. the work like one big card with
failover.