IOPS Question

[MySongRanHills]

Many people and articles throw around IOPS as if it is a standard term, but rarely do they specify block size, read/write % or how sequential vs random.

Usually it seems (to me at least) people are referring to a 4k block size, but as for the others when you see a products IOPS rating or someone tosses the term around what do you assume they mean for the others?

 

[staticlag]

Usually HD manufacturers will specify read/write, random/seq in fine print under IOPS.

Mostly it is just a measure of latency and people try and max it out with the settings that give the highest numbers.

 

[Chris_Lonardo]

4k is pretty standard for random IOPS, but you're right, it's worth checking the fine print.

Also of note is that IOPS alone, of course, isn't really a good way to evaluate a drive.

 

[MySongRanHills]

I was thinking less in terms of drives and more in terms of a NAS' rating or someone describing their own storages performance like "my nexenta system delivers 25,000 IOPS over iSCSI"

 

[staticlag]

I was thinking less in terms of drives and more in terms of a NAS' rating or someone describing their own storages performance like "my nextenda system delivers 25,000 IOPS over iSCSI"

Same, it is a measure of latency.

 

[MySongRanHills]

Same, it is a measure of latency.

So unless it is specifically stated there is no standard read/write rand/seq % one should assume ?

 

[Brahmzy]

When comparing storage vendors, you need to compare like metrics. One will say "Our array does 500,000 IOPS." Fine and great - the next vendor will say "Our array does 300,000 IOPS 4k block, 100% read."

Compare all arrays on the same page - configuration, usable capacity (after conservative data reduction (if applicable), IOPS, latency and R/W ratios at specific block sizes and all at what % to full.

Also, what is the maintenance schedule for the background work? Some arrays have all-the-time maintenance/garbage collection, some have a built-in schedule to perform this maintenance off peak hours. Some vendors will be very trixy with their answers, and this can be a very important thing, depending on it's impact to performance if you're a true 24/7 shop.