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ESXi HDD performance tuning

I have an ESXi 5 host, with windows 2008 svr and sql server 2005 (legacy application requires 2005 sql server)

The application running ok on when sql server 2005 installed on native OS, however, it is very slow if it is installed in vm.

I try to find out why. I use HD Tune pro to benchmark the HDD performance.

This is result of native OS with sql 2005


The HDD performance is very poor, but it can get jobs done.

The result of vm


Actually, the performance is much better than my native OS.

But I noticed in vm, it starts slow at beginning, and very fast after dozens of seconds later.

I re-run the test several times, the result it same, very slow at beginning, faster after.

This vm host is on lsi raid controller, I have another vm host, which is on sata HDD direct connect on motherboard without raid


same thing

I have a theory, since my application is not HDD I/O intensive, it only read/write sql server occasionally, it might be the query is right on the slow start part.

It looks like HDD is sleeping most of time, and need a wake up period when I/O is coming.

So I wonder is there some settings that I can tweak, make read time is faster at beginning?

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Are there other VMs on that datastore taking up I/O?  Are you able to see statistics on the SAN side to see how that volume is behaving on the SAN itself?

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