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richa3312
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‎04-06-2017 08:18 AM - edited ‎04-06-2017 08:39 AM

‎04-06-2017 08:18 AM - edited ‎04-06-2017 08:39 AM

Storevirtual 3200 Latency Issue

Hi All,

I'm wondering if anyone can help or has experianced a similar problem. Its a long post so please bear with me!

We have recently purchased a Storevirtual 3200 SFF 10GB unit.

Its currently configured with 7 x 10K SAS in 2 x 3 disk RAID 5 sets along with a spare. We have exported a single volume (network RAID 0) to a single host which uses the Microsoft ISCSI initiator with multipathing enabled (4 x 1Gb connections).

On this volume we are running a single VM using Hyper-V 2012 R2 the VM has nothing running on it, it doesn't even have its network connected.

There is no other workload currently on the unit.

With this setup we are experiancing high write latency to the storage.

The VM hosts reports 40-50ms latency on average to the exported volume.  Intermittantly the latency will drop to what we consider normal ie 1-2ms and will remain at this level for several hours before jumping back to the 40-50ms level. Within the VM the latency will be slightly higher and although it doesn't seem to cause any issues it does seem sluggish and would probably implode if any load was placed on it.

When we look at IOPS on the datastore we see 1-2 IOPS regardless of latency.

We have also tried connecting from other hosts and the same issues persists.

At first we thought we had a networking issue however we've realised that the latency is present in the performance charts on the Storevirtual itsself so this seems unlikley. Also when copying large files to the unit throughput is good and easily saturates 1Gb ethernet.

We have also noticed some strange behaviour when failing over between storage controllers. If we failover to either storage controller the latentcy dissapears when we failback the latency returns.

Oddly if we leave the controller failed over for a long period of time at some point the latency will return.

Out of interest we have run Microsofts Diskspd programs to check the IOPs on the unit and compared this to the drives on the host server.

On the host server which has 2 x 10K SAS SFF in RAID 1 with a 2GB FBWC (ar440) we see very high IOPS and throughput. If we disable the FBWC using HP SSA things look far more as we'd expect and vaguly inline with performance suggested by a RAID calculator for 2 10K disks in RAID 1.

The Storevirtual on the same test doesn't behaviour as if it has a write cache at all and performs inline with what a RAID calculator suggest for two RAID 5 arrays with a stripe.

Even without the cache I wouldn't expect to see this latency when there is no load on the unit in fact i wouldn't expect this on a single SATA drive!

Has anyone seen this before? Does anyone have a similar setup? Am I expecting too much? It just doesn't seem right to me.

I do have a case open with support but its slow and we keep going around in circles.


Thanks for looking!

PS I have graphs and screen shots which I will upload if I can work out how to!

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