Which EXP810's Disk Drive to choose?

[khalidaaa]

Hi All,

I'm in the process of upgrading our SAN DS4500.

I've the following options:

1) 16 x 73GB Disks

2) 8 x 146GB Disks

3) 4 x 450GB Disks

4) 4 x 300GB Disks

Now IBM salesperson is suggesting option 1 as it will provide the fastest transfer rate (because it is a smaller disk). But that option happened to be the most expensive one so Is there a penelty in choosing the other options? Is he correct?

Thanks

Regards,
Khalid

 

[LeeMason]

I don'th think I would go option 1. Apart from anything else it will take up a lot of disk slots. The 73GB disks are not faster in themselves but I guess his argument is around spreading the data across more spindles for performance. Track to track seek time and rotational latency of disks is less with the higher capacity disks so you will gain performance with the larger disks (on an individual disk basis) because data packing density is higher.

This will offset to some extent the benefits of more spindles. I would suggest option 2 or 3 might be best. Option 2 because it gives a higher (but not too high) number of spindles and option 3 because of the higher packing density of the 450GB drives.


Lee Mason
Optimal Projects Ltd

http://www.opl.co.uk

http://www.backupsanywhere.com

 

[khalidaaa]

Thanks LeeMason for your suggestions. Does the SAN cache matter in this case? I beleive the bigger the cache the better the disk performance regardless of the disks size! We have 1GB cache. Isn't it?

Regards,
Khalid

 

[p5wizard]

Not as much cache size, but cache-friendliness of your apps and cache-hit ratio.

If "it" is not in cache, "it" needs to be read from the backend disks, ergo the faster the disks and the mored spindles you have, the better.

Also your read/write ratio is important in regard to your cache size, because writes to cache need to be offloaded to the backend disks also.


HTH,

p5wizard