I don't know if someone have seen this before, it's pretty weird.

I have a virtual machine RHEL 6.5 running on a host Vmware ESXi 5.1, the storage being on a SAN IBM V700. A simple copy operation of a 1GB .iso file is generating a spike in latency, 10 ms or more.

I've tried several things:
- tweaking I/Os with tuned-adm even stopping completely the I/O scheduler with elevator=noop
- at VMware level - switching SCSI controllers, updating VMware tools and upgrading to the last hardware,

and with all these there is no change, the spikes in latency are there.
I don't see this on a Windows machine, just on Linux ones.

Any ideas of what is causing this?

After a lot of tests we figured ou that in reality there are no latencies even though the SAN monitoring tool provided by IBM was showing a totally different picture.
Problem solved.