[CentOS] Harware vs Kernel RAID (was Re: External SATA enclosures: SiI3124 and CentOS 5?)
Chan Chung Hang Christopher
christopher.chan at bradbury.edu.hk
Tue Jun 2 22:15:44 UTC 2009
> I've read a lot of different reports that suggest at this point in time,
> kernel software raid is in most cases better than controller raid.
>
Let me define 'most cases' for you. Linux software raid can perform
better or the same if you are using raid0/raid1/raid1+0 arrays. If you
are using raid5/6 arrays, the most disks are involved, the better
hardware raid (those with sufficient processing power and cache - a long
time ago software raid 5 beat the pants of hardware raid cards based on
Intel i960 chips) will perform.
I have already posted on this and there are links to performance tests
on this very subject. Let me look for the post.
> The basic argument seems to be that CPU's are fast enough now that the
> limitation on throughput is the drive itself, and that SATA resolved the
> bottleneck that PATA caused with kernel raid. The arguments then go on
>
Complete bollocks. The bottleneck is not the drives themselves as
whether it is SATA/PATA disk drive performance has not changed much
which is why 15k RPM disks are still king. The bottleneck is the bus be
it PCI-X or PCIe 16x/8x/4x or at least the latencies involved due to bus
traffic.
> to give numerous examples where a failing hardware raid controller
> CAUSED data loss, where a raid card died and an identical raid card had
> to be scrounged from eBay to even read the data on the drives, etc. -
> problems that apparently don't happen with kernel software raid.
>
>
Buy extra cards. Duh. Easy solution for what can be a very rare problem.
More information about the CentOS
mailing list