[CentOS] 3ware 9650 issues

Sun Jun 22 05:09:19 UTC 2008
Joshua Baker-LePain <jlb17 at duke.edu>

On Sun, 22 Jun 2008 at 1:01am, Ruslan Sivak wrote

> Joshua Baker-LePain wrote:
>> On Sat, 21 Jun 2008 at 9:12pm, John R Pierce wrote
>> 
>>> I have no experience with that raid card, most of our larger systems use 
>>> external SAN storage, but I will say that, IMHO, is a very large raid-6. 
>>> we usually don't make single raid sets much large than 7-8 drives, and for 
>>> a very large storage system, will stripe multiple raid5/6 sets rather than 
>>> have one huge one.
>> 
>> Would that I had such luxuries.  This is a university lab with needs for 
>> massive amounts of data and not much money with which to do it.
>> 
> Wouldn't striping a bunch of raid6 volumes give you about the same amount of 
> space?

No.  We have 24 drives.  Use one for a hot spare -> leaves 23.

1 array:  23 drives, - 2 for parity -> capacity = 21 * drive capacity
2 arrays: array1 = 12 drives - 2 for parity -> 10 drives
           array2 = 11 drives - 2 for parity -> 9 drives
                                     -> capcity = 19 * drive capcity
3 arrays: array1 = 8 drives - 2 for parity -> 6 drives
           array2 = 8 drives - 2 for parity -> 6 drives
           array3 = 7 drives - 2 for parity -> 5 drives
                                     -> capcity = 17 * drive capacity

With 1TB drives, you're losing 2TB worth of volume space for each 
increased number of arrays.  That's a lot of space.

Unless I misunderstood you...

-- 
Joshua Baker-LePain
QB3 Shared Cluster Sysadmin
UCSF