[clug] Hardware Assisted RAID (RAID through BIOS/Chipset RAID)

Paul Wayper paulway at mabula.net
Mon Oct 29 05:26:53 MDT 2012


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On 10/26/2012 10:46 AM, Edward C. Lang wrote:
> Hi,
> 
> On Wed, Oct 10, 2012 at 09:04:40PM +0200, Martijn van Oosterhout wrote:
>> But if, as you say, you only have 2 disks, chances are you don't need 
>> to spend the money on a good RAID controller, just go for Linux 
>> software RAID.  It's reliable and definitly faster that any random
>> BIOS controller you're likely to have.
> 
> Does anyone on the list have recent comparisons of the performance of 
> software RAID devices and LVM RAID volumes? I'm becoming a little 
> frustrated with the relative lack of flexibility of the former.

Performance measures?  Not to hand.  Rough guess: there won't be much in it.
 LVM basically supports RAID0 (striping) and RAID1 (mirroring).  It doesn't
do anything with parity, so it doesn't support the higher single-digit RAID
versions.  If you really want, you can make a PV of a mirrored LV, and use
two such PVs to create RAID10 storage using LVM.  I wouldn't bother, MD is
much better at this.

What I have done elsewhere is use MD to create RAID1 devices from two equal
partitions, and then use LVM to stripe data across them.  The lights
flashed, /proc/mdstat told me it works, it seemed fast, I didn't do any
benchmarks.

Ed, what is your actual load here?  You're obviously interested in
performance yet I'm wondering if the performance difference between RAID1
using LVM and RAID1 using MD is actually going to make any difference to
your real-world load; any more than, say, investing in more RAM, or spending
time optimising your application, or tuning your file system options.

Have fun,

Paul

P.S. LVM mirroring is also used to migrate storage from one PV to another
while the LV is active... which is pretty neat IMO.
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