Disk Arrays
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Storage config

Occasional Advisor

Storage config


If I have stats about the IO's occuring from my host to array ,how do go about and calculate the configuration details of my new storge ,as to how many RAID groups i will require ,using (15 krpm or 10 krpm disk ),where should I keep the application and where the data ? Which size lun should I create to effetively distribute data etc ...
How will the HP guys can help me in this ?

thanks in advance.....
Matt Burgess
Frequent Advisor

Re: Storage config

First question: what is the storage?

Yes. This matters.

With regard to 10k v 15k: always choose 10k drives (unless you're only buying 1-3) and buy more of them. The #1 factor in determining perfomance will be the of drives. ie. 6x10k > 4x15k. for a sililar price.

With regard to your RAID arrays: the RAID level itself will have an impact, but you can think of a 10k drive as providing 100iops (eg. Oracle@8k = 800kbps) and a 15k drive somewhere between 120-150iops (depends if it's SCSI, SAS, FC etc). Uae those numbers to estimate.

Remember - RAID 0 will give you this raw performanc, but RAID 1/0 will probably only give you 4/5 of this performance and RAID 5 somewhere between 1/2 - 2/3 of the performance (RAID5 with =<4 disks is pretty bad).
Nigel Poulton
Respected Contributor

Re: Storage config

Hi avamar,

The formula for working our IOPs for a single disk is as follows -

(1/(av_seek_time + av_latency))*1000

So for a Seagate Cheetah 15K disk it is as follows -

(1/(3.5 + 2.0))*1000 = 181 Max IOPs

Remember though that this is max and you cant really max your disk especially for random I/O as this will cause severe thrashing...... try and keep your IOPs below 60% and definitely below 70%.

Of course the above applies to the disks themselves without cache assistance (e.g. random reads). You will get the benefits of cache for most other workload types.

As for RAID groups choice. The more disks the better is indeed good advice. The following though is a rough guide as to how different RAID configurations work on XP storage -

If you assume that RAID1 (2+2) is your baseline, then the following general guidelines apply -
RAID1 (4+4) will be double the performance for all workload types
RAID5 (3+1) will perform about half as well for random writes and about 1.5 times better for sequential writes
RAID5 (7+1) will perform about the same for random writes but around 3 times better for sequential writes.

These are rough guidelines.

Hope this helps,


Talk about the XP and EVA @ http://blog.nigelpoulton.com