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Re: PowerEdge 2950 questions

From: "Bucky Jordan" <bjordan(at)lumeta(dot)com>
To: "Jeff Davis" <pgsql(at)j-davis(dot)com>,<pgsql-performance(at)postgresql(dot)org>
Subject: Re: PowerEdge 2950 questions
Date: 2006-08-22 21:56:12
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Lists: pgsql-performance
Hi Jeff,

My experience with the 2950 seemed to indicate that RAID10x6 disks did
not perform as well as RAID5x6. I believe I posted some numbers to
illustrate this in the post you mentioned. 

If I remember correctly, the numbers were pretty close, but I was
expecting RAID10 to significantly beat RAID5. However, with 6 disks,
RAID5 starts performing a little better, and it also has good storage
utilization (i.e. you're only loosing 1 disk's worth of storage, so with
6 drives, you still have 83% - 5/6 - of your storage available, as
opposed to 50% with RAID10). 

Keep in mind that with 6 disks, theoretically (your mileage may vary by
raid controller implementation) you have more fault tolerance with
RAID10 than with RAID5.

Also, I don't think there's a lot of performance gain to going with the
15k drives over the 10k. Even dell only says a 10% boost. I've
benchmarked a single drive configuration, 10k vs 15k rpm, and yes, the
15k had substantially better seek times, but raw io isn't much
different, so again, it depends on your application's needs.

Lastly, re your question on putting the WAL on the RAID10- I currently
have the box setup as RAID5x6 with the WAL and PGDATA all on the same
raidset. I haven't had the chance to do extensive tests, but from
previous readings, I gather that if you have write-back enabled on the
RAID, it should be ok (which it is in my case).

As to how this compares with an Opteron system, if someone has some
pgbench (or other test) suggestions and a box to compare with, I'd be
happy to run the same on the 2950. (The 2950 is a 2-cpu dual core 3.0
ghz box, 8GB ram with 6 disks, running FreeBSD 6.1 amd64 RELEASE if
you're interested in picking a "fair" opteron equivalent ;)



-----Original Message-----
From: pgsql-performance-owner(at)postgresql(dot)org
[mailto:pgsql-performance-owner(at)postgresql(dot)org] On Behalf Of Jeff Davis
Sent: Tuesday, August 22, 2006 5:34 PM
To: pgsql-performance(at)postgresql(dot)org
Subject: [PERFORM] PowerEdge 2950 questions

This question is related to the thread:
but I had some questions.

I am looking at setting up two general-purpose database servers,
replicated with Slony. Each server I'm looking at has the following

Dell PowerEdge 2950
- 2 x Dual Core Intel(r) Xeon(r) 5130, 4MB Cache, 2.00GHz, 1333MHZ FSB
- PERC 5/i, x6 Backplane, Integrated Controller Card (256MB battery-
backed cache)
- 6 x 73GB, SAS, 3.5-inch, 15K RPM Hard Drive arranged in RAID 10

These servers are reasonably priced and so they seem like a good choice
for the overall price, and the above thread indicated good performance.
However, I want to make sure that putting WAL in with PGDATA on the
RAID-10 is wise. And if there are any other suggestions that would be
great. Is the RAID controller good? Are the processors good for database
work or are Opterons significantly better?

I may go for more storage as well (i.e. getting 300GB disks), but I am
still determining the potential need for storage. I can get more RAM at
a later date if necessary also.

	Jeff Davis

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