High write latency on tempdb datafiles only I'm experiencing large write latency on our tempdb database, but on no other database.
(from sys.dm_io_virtual_file_stats) Tempdb log file latency is also listed as being below 5ms.

For comparison:
Write latency on all databases except tempdb are below 5ms, tempdb was about 500ms when using 8 datafiles. I removed 4 datafiles 2 days ago just to check if something changes and it looks like the latency doubled after doing this.

A few notes on our environment:


SQL Server 2008 R2 SP3 VM running on Hyper-V
one large RAID10 array attached to our Hyper-V hosts via fibre channel where everything is stored


I have no explanation for this and I don't know where to look for answers.
I could of course assume that doubling the data files will half the WriteLatency but I don't know if this is the way to go.

Any ideas on where to start?
I seem to have solved it or at least know where it is coming from.

To find out I setup perfmon to monitor avg. ms per write operation and it looks like this. which leads me to the conclusion that those extreme spikes only happen during nightly index rebuilding (I'm using Ola Hallengrens IndexMaintenance-solution for this), normal operation is fine.

My learning: don't rely on cumulated stats in sys.dm_io_virtual_file_stats only, but they are a good indicator to look further for the origin.