Migrating from ide to virtio does not increase speed on some virtual machines

[dobriivoin]

Replaced on some VM'S virtual hard drives from IDE to VirtIO.


/Etc/pve/qemu-server/files *. CONF. replaced these strings:
bootdisk: ide0: instead of virtio0


virtio0: local: 105/vm-105-disk-1.qcow2, size = 10 g


Speed boost was pleasantly surprised. But on some machines, speed is not changed:


hdparm-t/dev/vda768 MB in 3.00 seconds = 255.58 MB/sec


and


hdparm-t/dev/sda 768 MB in 3.00 seconds = 260.58 MB/sec


that is almost the same.


On the same machine where all was "excellent":


hdparm-t/dev/vda 768 MB in 3.00 seconds = 760.58 MB/sec


Understand that the problem is in the VM. But I cannot understand why the VM's seem to perceive that works with virtio-driver. On machines installed ubuntu server 12.04 LTS.

The format of the virtual volume's are raw.

All virtual disks are on the same real storage( raid10)

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How to solve this problem?

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[udo]

Replaced on some VM'S virtual hard drives from IDE to VirtIO.


/Etc/pve/qemu-server/files *. CONF. replaced these strings:
bootdisk: ide0: instead of virtio0


virtio0: local: 105/vm-105-disk-1.qcow2, size = 10 g


Speed boost was pleasantly surprised. But on some machines, speed is not changed:


hdparm-t/dev/vda768 MB in 3.00 seconds = 255.58 MB/sec


and


hdparm-t/dev/sda 768 MB in 3.00 seconds = 260.58 MB/sec


that is almost the same.


On the same machine where all was "excellent":


hdparm-t/dev/vda 768 MB in 3.00 seconds = 760.58 MB/sec


Understand that the problem is in the VM. But I cannot understand why the VM's seem to perceive that works with virtio-driver. On machines installed ubuntu server 12.04 LTS.

The format of the virtual volume's are raw.

All virtual disks are on the same real storage( raid10)

​

​

How to solve this problem?

​

​

Hi,
I don't know how good the measurements from hdparm is, but perhaps you measure caching with the 760MB/s?
Are all disk setting the same (cache=none or what else)?
All disk-format the same (qcow2)?

How fast is your raid-10? 760MB/s looks not bad... if you have an raid-10 with 6 hdds, you can read app. 3 (one side of the mirror) * 120MB/s (how fast your disks are) = 360 MB/s.
Of course, a raidcontroller can read from all disks, but then it's need more time for seek (no continues reading, because the next data will read be the other side of the mirror) - I guess that's bring no benefit.
E.G. for 760MB/s with normal HDDs you nedd app. 12 disks?!

Udo