we run several windows servers and windows clients on our vmware esx. One of the Windows 2003 Servers is a build-server with major HDD-reads/writes. as it is our build server.

This machine was a hardware before and was virtualized to the ESX. Is there any way to increase the HDD-Performance? Perhaps there are special windows (guest) drivers? The files are stored on a Raid6 base.

Performance graph of vmware infrastructure client shows reads up to 650 KBps and writes up to 4000 KBps.

Thank you. Regards, Uwe

  • The performance you indicate appears to be extremely poor but a lot depends on the type of IO requests that are being made when you take those performance numbers. Do you know what the IOPS load your combination of VM's should typically generate? And what sort of IOPS can your disk setup provide? Some more info on the exact hardware setup would be useful - type of storage subsystem, controller make\model, no and type of disks. Also the amount of RAM, Qty and speed of CPU's and total RAM. How many and what spec are the other VM's etc. – Helvick Oct 13 '09 at 20:06

If you have the latest VMTools on there then there's little within the guest you can do but if you can move its data to a faster (RAID10?) array you should see some significant speedup over the RAID6 setup you have now. You also shouldn't write off a V2P conversion, some people seem shocked at the thought but it really is the only route for certain classes of server usage.

Edit - oh and you could always consider moving to V4 if you're on V3.5, it really is that much quicker.

  • The only thing I would add to Chopper's answer is make sure you are not ballooning memory on any of your VMs. Writing memory to disk will eat IOPs for breakfast. – JakeRobinson Mar 12 '11 at 4:43
  • If you have the drives and bays you could also setup a Datastore only for this VM. That would give it almost full speed access to the drives. – Scott Keck-Warren Mar 14 '11 at 12:10

Making sure that the virtual disks aren't sharing a lot of physical disks could help, too :)

And to second @Chopper3, sometimes physical is better.

You might also look at using non-virtual drives for that particular server and giving them direct drive access instead.

  • 2
    Maybe it's just me but I've never really found RDMs that much faster than well planned VMDKs. That said you did remind me that he should kick every other VM out of the LUN he's using to minimise SCSI reservation locks, thanks. – Chopper3 Sep 22 '09 at 12:24

ESX 4.x have a new paravirtualized SCSI controller called "VMware Paravirtual". I never tried it on Windows but on Linux it gives a significant io bust. You can give it a try and let us know if it helps.


I also had this problem when first diving into ESXi some years ago. Two factors seriously impacted performance:

BBWC was the big one. On ProLiant servers with Smart Array cards, adding a battery backup (

Partition alignment was good for a ~15% performance boost on sequential I/O. Random was not really affected. VMWare's white paper shows similar results in a controlled environment.

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