Hi Gerald,

I think you have to consider that if you use RAID5 logical drives, you have
to calculate and write a parity every time you write any data on the disk:
so if you have a write intensive application, RAID5 is not so efficient as
other RAID protections (1,10, etc); if you have instead read-intensive
applications RAID 5 is a good choice because it gives you the possibility
to use more physical drives concurrently.
Furthermore RAID 5 is the most efficient protection regarding the optimal
usage of the available phisical capacity, and it is more and more efficient
as the number of physical drives in the array increase; but at the same
time as the number of physical drives increase, the performance goes down
(because you have to calculate the parity on a larger number of blocks):
probably the best compromise is a number of 7/8 disk drives/array.
I hope this helps.



Cordiali saluti / Best regards

Gianluca Perilli



Gianluca Perilli
Tivoli Customer Support
Via Sciangai n° 53 - 00144 Roma (Italy)
Tel. 06/5966 - 4581
Cell. 335/7840985


                                                                                
                                                       
                      Gerald Wichmann                                           
                                                       
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Since a RAID-5 array shows up as one big filesystem, what's the best
strategy for determining how many and of what size disk pool volumes to
create for your primary disk storage pool? For the most part I don't think
it really matters unlike allocating volumes on individual disks but perhaps
I'm not considering something.

Thanks..