Va7100 and mixed size disks

[Tim Killinger]

I'm planning to add disks to my qty 11 15k 18gb disk VA7100 (before we've even been in production!)

Are there performance considerations if I choose to add, say 4 more 72gb drives mixed with the existing 18gb drives?? In other words, does the dramtic differencd in spindle capacitiy of the drives I'm adding affect overall performance?

Would I be better off adding like size drives (18gb) assuming capacity needs are met??

Thank you very much!!!

[Eugeny Brychkov]

Tim,
I do not think you'll have perfomance increase or decrease. All disks are on the same FC-AL, and data is distributed across all these disks, and, if reading disks in parallel, data will be gathered according to slowest disk (that's my point of view).
Adding 4 disks is good idea - not 1 and even 2 disks. As I already stated all data are spread across all disks, and if you'll insert one larger disk, where VA firmware will be mirroring highest disk blocks? These blocks will be used for read cache
Eugeny

[paul courry]

Eugeny, I'm not sure I agree.

Adding 72Gb disks to a bunch of 18Gb disks ensures that the 72's hold most of the data and will become a bottleneck on the system because of the throughput limit on the 72Gb disks.

He would most definitely be better off to add 18's in the amount he needs as this adds more spindles to the volume. More spindles means more throughput. 4 18's have more throughput than 1 72.

[Eugeny Brychkov]

Definitely do not agree. Adding 4x72GB is better than adding 4x18GB.
From the reliability point of view I agree there can be bottleneck if adding 3x72GB disks, but not 4x72GB disks. Four disks is ENOUGH for VA to use fully redundant, reliable storage data allocation method (remember - minimal number of disks in VA7100 is 4 disks, so using 4 disks min VA uses reliable data allocation method)
Eugeny

[Tim Killinger]

I do have an issue in that I can only add 4 more drives, whatever their capacity (I currently have 11 18gb drives).

Therefore I would PREFER to add bigger drives, but if performance is negatively affected, I wanted to be aware.

[paul courry]

Dueling crowns I guess, though I think we are arguing apples and oranges.

Just remember, whatever your decision, you can always yank 18's later and sell them and upgrade by replacing them with 72's. There is a good market for used 18's.