SSD MS Latency vs IOPS

[Alyx]

Hi,

I'm trying to find a graph that shows how SSD latency scales up as IOPS increases. I assume as the disks get more IOPS the latency would slowly scale up but I can't find any graphs to confirm this.

The closest I've found is here:
http://www.storagereview.com/intel_ssd_dc_s3700_series_enterprise_ssd_review

Which shows MS latency vs the # of test threads, but not the underlying IOPS.

Has anyone seen numbers like these?

 

[Emulex]

IOPS is just transfer rate.

You want to know at what transfer rate latency goes up? that's complicated depending on what you are doing (read/write - erase/trim/etc).

What are you actually trying to work out?

 

[Alyx]

We have a server side application that has fairly tight tolerances to read latency, we need reads to be always under 5ms, 10ms at the absolute worst. And given x number of servers with X number of drives how many IOPS can we handle before latency falls out of tolerances.

I'm working on setting up a test bed now, but if I had a graph that showed read latency vs IOPS just for single SSD it would help a lot in knowing what we could handle and help me frame my test. IE:

if a normal SSD's latency scales linearly as IOPS increase it would be different from having it be an exponential graph where they can handle a lot of IOPS at a specific latency and then there being a threshold where latency increases very quickly.

 

[glugglug]

What you are saying makes no sense.

Latency is a measure of time. (so it can be expressed in units like s, ms, etc.)
IOPS is a frequency . (so it can be expressed in units of Hz, kHz, MHz, etc).

I think maybe you are confusing IOPS with queue depth (which for the synthetic tests, queue depth should be the same as # of test threads).

So if anything, latency and IOPS are going to be INVERSELY proportional.
Assuming the test runs as fast as possible on each thread (why wouldn't it?),
latency = QD (queue depth or thread count) / IOPS (assuming you are throwing as many IOPS at it as possible limited by the response time and your thread count).