Re: Another RAID controller recommendation question

On 06/18/2011 02:46 AM, David Boreham wrote:
>
> We're looking to deploy a bunch of new machines.
> Our DB is fairly small and write-intensive. Most of the disk
> traffic is PG WAL. Historically we've avoided
> RAID controllers for various reasons, but this new deployment will be
> done with them (also for various reasons ;)

If the traffic is heavy on WAL, avoiding RAID controllers isn't a great
practice.  They're by far the best way possible to speed that up.

> http://www.newegg.com/Product/Product.aspx?Item=N82E16816101339
> manufacturer page :
> http://www.supermicro.com/products/system/1U/6016/SYS-6016T-URF4_.cfm?UIO=N
>

This a solid basic server model.  The Intel 5520 chipset they're built
on is nice and fast if you load it up with a bunch of RAM.

> these boxes have a proprietary controller slot, with these cards:
> http://www.supermicro.com/products/nfo/UIO.cfm#Adapters
> specifically this LSI-based one which seems to be the newest/fastest,
> with BBWBC:
> http://www.supermicro.com/products/accessories/addon/AOC-USAS2LP-H8iR.cfm

I don't really like the whole proprietary controller slot thing if it
can be avoided.  We seem to have a lot of customers buying from Dell
recently, and it's partly because they've made it pretty straightforward
to swap out their PERC controller.  That makes troubleshooting a broken
server easier, spare parts are simple to manage, lots of advantages.
You almost need to stock your own spares for things like the RAID cards
if they're these propriety slot ones, because you're unlikely to find
one in an emergency.

That said, the card itself looks like plain old simple LSI MegaRAID.
Get the battery backup unit, check the battery and cache policy to make
sure they're sane, and learn how to use megaci to monitor it.  Fast and
generally trouble free after that initial setup time investment.


> These machines are operated in a lights-out mode, and
> will handle heavy constant load (hundreds of write txn/s) with 15K SAS
> drives
> in a RAID-1 setup (2 drives, or 2 + 2 with data and WAL split between
> spindle groups).

If you can try to measure the exact ratio of database to WAL traffic
here, that might help guide which of these configurations makes more
sense.  Hard to answer in a general way.

--
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
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