[CentOS] Harware vs Kernel RAID (was Re: External SATA enclosures: SiI3124 and CentOS 5?)
Michael A. Peters
mpeters at mac.com
Tue Jun 2 02:52:59 UTC 2009
-=- starting as new thread as it is off topic from controller thread -=-
Ross Walker wrote:
> The real key is the controller though. Get one that can do hardware
> RAID1/10, 5/50, 6/60, if it can do both SATA and SAS even better and
> get a battery backed write-back cache, the bigger the better, 256MB
> good, 512MB better, 1GB best.
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.
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
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.
The main exception I've seen to using software raid are high
availability setups where a separate external unit ($$$) provides the
same hard disk to multiple servers. Then the raid can't really be in the
kernel but has to be in the hardware.
I'd be very interested in hearing opinions on this subject.
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