performance difference betwee 73 GB and 146 GB hard disk in virutal array

[Jawed Akhtar]

Hi,
We are going to buy on storage array with 2 TB capacity.
which size of disk are better with reference to performance and price. Is it better to buy low capacity disk to have better I/O.
what would be ratio between cost and perfoemnace if low capacity disks I/O is better than high capacity disks.

Thanks in Advacne.
REgd
JAwed AKhtar

[Zygmunt Krawczyk · Accepted solution]

I assume that you consider EVA 3000. EVA supports 73GB HDD 15k, 73GB HDD 10k, 146GB HDD 10k. If you need 2TB raw capacity, the solution might be:

1. 28 x 73GB 15k (best performance)
2. 28 x 73GB 10k (lower performance, lower price)
3. 14 x 146GB 10k (lower performance, lowest price)

General rule is higher number of disks higher performance.

Regards,
Zygmunt

[Ted Buis]

I would say #3 is lowest performance and lowest price. Funny how it always works that way. Spindles count when it comes to performance even with a VA or EVA. However, as you get more and more drives in group, you do get diminishing returns, so once the array has 50+ drives on a VA7410 you might switch to some of the higher density drives. On the EVA, it depends on how many drives you form into the group. Naturally, your mileage will also vary based on the application and the RAID level. If you use, AutoRAID on the VA then it will depend also on how much data you put in. If it is less than 50%, then most everything is mirrored and performance is at a maximum. This then raises the question of whether you are better off with mirrored disk in the array with larger slower disks, or RAID 5 with smaller faster disks. Again it depends. RAID 5 will always have a write penalty.
So best performance is with the most drives, at the highest rotation rate, and mirrored, so that you get the least usable capacity. I have even seen where drives were added to reach the desired performance level even when the capacity was not needed! So, unless you know how many IOPs you need, the best thing to do is make an educated guess, and be prepared to add disks if performance is insufficient.