<br><br><div class="gmail_quote">On Tue, May 24, 2011 at 10:42 AM, The Don Lachlan <span dir="ltr"><<a href="http://ale-at-ale.org">ale-at-ale.org</a>@<a href="http://unpopularminds.org">unpopularminds.org</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div class="im">On Tue, May 24, 2011 at 07:37:16AM -0400, LinuxGnome wrote:<br>
> I would go with many 15k drives for the data (for example, if you have a 500G DB, then 9x 73G drives in RAID5 will you 6~8 times the performance of one 600G drive that is IO bound). You might consider a ramdrive (i.e. FlashCache, not SDD) for writing your logs to.<br>
<br>
</div>Do NOT use RAID5. Ever. For ANYTHING. Unless you're trying to show exactly<br>
how much it sucks in comparison to RAID10.<br>
<br>
<a href="http://www.miracleas.com/BAARF/RAID5_versus_RAID10.txt" target="_blank">http://www.miracleas.com/BAARF/RAID5_versus_RAID10.txt</a><br>
<a href="http://www.zdnet.com/blog/storage/why-raid-5-stops-working-in-2009/162" target="_blank">http://www.zdnet.com/blog/storage/why-raid-5-stops-working-in-2009/162</a><br>
<br>
If you are absolutely wedded to parity, use RAID6. But really, you should<br>
still use RAID10.<br>
<br>
<a href="http://storagemojo.com/2010/02/27/does-raid-6-stops-working-in-2019/" target="_blank">http://storagemojo.com/2010/02/27/does-raid-6-stops-working-in-2019/</a><br>
<br>
The math is already out there. In RAID5, you can only survive one disk<br>
failure - two concurrent disk failures and you're dead. RAID10 may fail<br>
after two concurrent disks failures but it can survive up to n/2 disk<br>
failures, depending which disks fail, and the odds are higher that drives in<br>
different mirrors will fail rather than in the same mirror.<br>
<br>
Then, you want to rebuild. In RAID5, you have to read from n-1 disks to<br>
rebuild, whereas RAID10 requires you to read 1 disk. As disks increase in<br>
size, the probability of a read error during a rebuild approaches 100%,<br>
which is more likely under RAID5 than RAID10 because you're reading more<br>
disks and more data. Read error == failed rebuild. Some current drives are<br>
large enough that it is a certainty in a RAID5 rebuild.<br>
<br>
Do. NOT. Use. RAID5.<br></blockquote><div><br>+100<br><br>RAID5 was designed for when hard drives were REALLY FREAKING EXPENSIVE. RAID5 needs to die. RAID6 needs to join it. <br><br>If you're really data paranoid, triple mirror RAID1 with RAID0 stripe for speed. Makes the rebuilds fly from a user perspective. <br>
6-drive RAID10 SAS will saturate a single PCIe x8 bus on a read :-) So build 2 sets (12 drives) and use another card :-D<br></div><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<font color="#888888"><br>
-L<br>
</font><div><div></div><div class="h5">_______________________________________________<br>
Ale mailing list<br>
<a href="mailto:Ale@ale.org">Ale@ale.org</a><br>
<a href="http://mail.ale.org/mailman/listinfo/ale" target="_blank">http://mail.ale.org/mailman/listinfo/ale</a><br>
See JOBS, ANNOUNCE and SCHOOLS lists at<br>
<a href="http://mail.ale.org/mailman/listinfo" target="_blank">http://mail.ale.org/mailman/listinfo</a><br>
</div></div></blockquote></div><br><br clear="all"><br>-- <br>-- <br>James P. Kinney III<br><br>As long as the general population is passive, apathetic, diverted to
consumerism or hatred of the vulnerable, then the powerful can do as
they please, and those who survive will be left to contemplate the
outcome.<br>- <i><i><i><i>2011 Noam Chomsky</i></i></i></i><br>