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