[CentOS] 4 X 500 gb drives - best software raid config for a backup server?
Les Mikesell
lesmikesell at gmail.com
Sat Feb 21 17:05:44 UTC 2009
Chan Chung Hang Christopher wrote:
>
>> We were talking about RAID1; RAID5/6 is a different area. Linux software
>> RAID1 is a safeguard against disk failure; it's not designed for speed
>> increase. There is a number of things that could be improved in Linux
>> software RAID; read performance of RAID1 is one of them - this _is_ why
>> some hardware RAID1 adapters indeed are faster than software.
>> Read http://kernelnewbies.org/KernelProjects/Raid1ReadBalancing - since
>> the 2.6.25 kernel a simple alternating read is implemented, but that
>> does not take the access pattern into account.
>>
> I have not read that yet but that is odd since I have been blasted by
> others before for doubting md raid1 doing multiple disk reads.
I know current centos alternates because I had a box with bad memory
corrupt a raid1 filesystem and after fixing it and fsck'ing the disk,
errors would slowly re-appear as they were hit on the alternate disk
that previous fsck runs had not seen.
To really speed things up, you would want to try to avoid seeks. A
simple alternating pattern may let the heads be in different places on
small reads, but for a large file you will end up doing the same head
motions on both drives (wasting the same time) as the reads alternate.
--
Les Mikesell
lesmikesell at gmail.com
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