Slow write speeds in VM's! Tried 4 different hard drives - all the same.

[Lokytech]

HDD R/W speed are mostly linked to your hardware, not the emulation type of the KVM drive.

As you can see in the above posts, just the cache=none option change the performance for 3flight.

What's your hardware ? SAN iSCSI ? NFS ? Local drive ?
In my case, NFS with raw format, the cache=none option reduce the IO speed, but i still have between 70MB/s to 250MB/s (thx to cache)

 

[dswartz]

true, but if possible, there is no reason not to use virtio vs scsi/ide, since there is less emulation overhead, no?

 

[camel]

Question how can I change the IDE to Virtio into a SME server?

http://pve.proxmox.com/wiki/Paravirtualized_Block_Drivers_for_Windows

Found what I needed here to change an existing disk from IDE to VIRTIO. It worked with Windows XP and 2008R2 guests.

 

[dswartz]

SME is a linux distro though, no?

 

[camel]

Sorry, it is a linux distro, missed that one.

Same principle applies though, just with a little modification. Guest Linux OS with kernel >= 2.6.25 should be OK. I've applied this method to several debian based servers that started out with IDE HDDs. The debian guests didn't complain that the bus had changed.

SME is based on CentOS (RedHat) so may have the virtio drivers in the kernel. But RedHat may have separate virtio drivers for CentOS/SME as kernel numbering is slightly different for RedHat.

Modified Linux procedure for changing block device drivers:
Shutdown the VM guest (SME in this case), in the hardware section of the VM delete the HDD (it just detatches the hdd file or LV from the VM), then add a new HDD using an existing virtual disk (lets you reattach the HDD), set BUS to VIRTIO, add.

Always backup before though..