<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
</head>
<body bgcolor="#ffffff" text="#000000">
It would be insane to hook up 12 drives in a RAID5. If you lose a
drive, it's gonna take a day to rebuild the array and what happens if
you lose a second drive while you're rebuilding? 4 x 250GB drives in
RAID 5 took about 10 hours to rebuild. It is probably quicker to
format and re-install. I hope you have backups.<br>
<br>
I use RAID 1+0 for database servers. For a app, file, or mail server,
I do RAID 1 unless I needed the space, then I'd do RAID 6. I don't run
RAID 5 on any of my servers anymore because I need redundancy beyond
losing 1 drive and the write performance blows.<br>
<br>
I should note that you can get sufficient performance from a RAID 5/6
by using a controller with 256MB of cache and allocated most of it to
write-back cache. Also, you should have a lot of RAM to cache database
pages in RAM and cache queries to avoid hitting the disk.<br>
<br>
-Chris<br>
<br>
<br>
Bret Baptist wrote:
<blockquote id="mid_200805281511_30877_bbaptist_iexposure_com"
cite="mid:200805281511.30877.bbaptist@iexposure.com" type="cite">
<pre wrap="">On Wednesday 28 May 2008 1:47:32 pm Josh Paetzel wrote:
</pre>
<blockquote id="StationeryCiteGenerated_1" type="cite">
<pre wrap="">On Wednesday 28 May 2008 11:14:50 am Justin Krejci wrote:
</pre>
<blockquote id="StationeryCiteGenerated_2" type="cite">
<pre wrap=""><a class="moz-txt-link-freetext" href="http://download.intel.com/support/motherboards/server/srcsas18e/sb/axxrpc">http://download.intel.com/support/motherboards/server/srcsas18e/sb/axxrpc</a>
m2 _ tps_10.pdf
Benefits are identified in this PDF.
Data caching (write-back cache can greatly improve write performance)
Busy databases servers commonly need lots of I/O
Also consider running RAID10 if you have drive availability (4 drive
minimum) as you will get much higher I/O performance with that as well
especially with writes. Though if you need the capacity, RAID5 will give
you one drive more of capacity. RAID10 can also give you a smaller chance
of data loss due to drive failures as you can potentially lose up to half
of your drives and still operate whereas using RAID5 and losing 2+ drives
= disaster.
</pre>
</blockquote>
<pre wrap="">Somewhere a DBA just rolled over in his grave at the mention of a database
using RAID 5. If you're ever going to care about performance at all don't
use RAID 5. It's particularly slow at the sorts of write I/O database
systems typically generate.
</pre>
</blockquote>
<pre wrap=""><!---->
For the most part this is true, however on a lot of modern RAID controllers if
you hook 12 drives up in RAID-5 you are going to see amazing performance.
Here is an article with a very thorough review of 9 SATA RAID cards:
<a class="moz-txt-link-freetext" href="http://tweakers.net/reviews/557/26/comparison-of-nine-serial-ata-raid-5-adapters-pagina-25.html">http://tweakers.net/reviews/557/26/comparison-of-nine-serial-ata-raid-5-adapters-pagina-25.html</a>
The issue here is that they do not do a RAID-10 test with 12 drives.
I don't know what they are doing on the Coraid SR 1521 to make RAID-5 faster
than RAID-10, but when you get up to 14 drives in the chassis you get much
better throughput, now mind you this is not random I/O, just another thing to
think about:
<a class="moz-txt-link-freetext" href="http://coraid.com/support/sr/ANSR002.pdf">http://coraid.com/support/sr/ANSR002.pdf</a>
For a large number of drives in a RAID-5 you get really good performance and
much higher capacity.
Not that this is really relevant to the original poster.
Thanks.
</pre>
</blockquote>
<br>
</body>
</html>