Re: Dell Hardware Recommendations

On 8/9/07, Joe Uhl <joeuhl@gmail.com> wrote:
> We have a 30 GB database (according to pg_database_size) running nicely
> on a single Dell PowerEdge 2850 right now.  This represents data
> specific to 1 US state.  We are in the process of planning a deployment
> that will service all 50 US states.
>
> If 30 GB is an accurate number per state that means the database size is
> about to explode to 1.5 TB.  About 1 TB of this amount would be OLAP
> data that is heavy-read but only updated or inserted in batch.  It is
> also largely isolated to a single table partitioned on state.  This
> portion of the data will grow very slowly after the initial loading.
>
> The remaining 500 GB has frequent individual writes performed against
> it.  500 GB is a high estimate and it will probably start out closer to
> 100 GB and grow steadily up to and past 500 GB.
>
> I am trying to figure out an appropriate hardware configuration for such
> a database.  Currently I am considering the following:
>
> PowerEdge 1950 paired with a PowerVault MD1000
> 2 x Quad Core Xeon E5310
> 16 GB 667MHz RAM (4 x 4GB leaving room to expand if we need to)
> PERC 5/E Raid Adapter
> 2 x 146 GB SAS in Raid 1 for OS + logs.
> A bunch of disks in the MD1000 configured in Raid 10 for Postgres data.
>
> The MD1000 holds 15 disks, so 14 disks + a hot spare is the max.  With
> 12 250GB SATA drives to cover the 1.5TB we would be able add another
> 250GB of usable space for future growth before needing to get a bigger
> set of disks.  500GB drives would leave alot more room and could allow
> us to run the MD1000 in split mode and use its remaining disks for other
> purposes in the mean time.  I would greatly appreciate any feedback with
> respect to drive count vs. drive size and SATA vs. SCSI/SAS.  The price
> difference makes SATA awfully appealing.

I'm getting a MD1000 tomorrow to play with for just this type of
analysis as it happens.  First of all, move the o/s drives to the
backplane and get the cheapest available.

I might consider pick up an extra perc 5/e, since the MD1000 is
active/active, and do either raid 10 or 05 with one of the raid levels
in software.  For example, two raid 5 volumes (hardware raid 5)
striped in software as raid 0.  A 15k SAS drive is worth at least two
SATA drives (unless they are raptors) for OLTP performance loads.

Where the extra controller especially pays off is if you have to
expand to a second tray.  It's easy to add trays but installing
controllers on a production server is scary.

Raid 10 is usually better for databases but in my experience it's a
roll of the dice.  If you factor cost into the matrix a SAS raid 05
might outperform a SATA raid 10 because you are getting better storage
utilization out of the drives (n - 2 vs. n / 2).  Then again, you
might not.

merlin