[Lustre-discuss] Hardware or software RAID?

Kevin Van Maren Kevin.Vanmaren at Sun.COM
Sat Nov 29 17:08:19 PST 2008


Hey Jeff,

Smaller _drives_ usually have shorter rebuild times, but having _fewer_ 
drives normally
makes little difference to rebuild times.  Both a 4+1 and an 8+1 need to 
write out "1 drive"
worth of data to the replacement drive (and read every other drive in 
the raid set once,
but those are all in parallel).

Kevin


Jeff Layton wrote:
> Andreas Dilger wrote:
>   
>> There are a number of large clusters (TACC Ranger in particular) that use
>> software RAID on JBODs, but the majority of systems use hardware RAID in order to
>> maximize performance (at an increased cost of course).
>>
>> These days I would tend to recommend using RAID-6 over RAID-5 just because
>> the large disks available take a long time to rebuild, and there is a
>> non-zero risk of a second disk failing during that time.
>>   
>>     
>
> What about using more, but smaller raid groups? For example,
> perhaps 4-5 drives in a RAID-5? That way if a disk fails, the
> rebuilds are faster since there is less data?
>
> Jeff
>
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