# [OmniOS-discuss] KVM - copy paste in VM

Bob Friesenhahn bfriesen at simple.dallas.tx.us
Wed Jul 30 14:12:47 UTC 2014

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    On Wed, 30 Jul 2014, Machine Man wrote:

    > The problem was making a copy of a large file inside the VM (duplicating the file in the VM)It was very slow and
    > it looks like it is the ide device.
    > Changed the controller to virtio and it is much faster.
    > I tried using an image file for this disk, but this was slower than pointing to zvol on ide.  I will test with
    > the controller set to virtio and file img for disk.
    > Overall,it is not bad now and the virtual machine is much more usable when making large copies, still seems slow
    > from what I would expect. Copy start off at 120MB/s and quickly drops down to 14MB/s and then jumps up and down
    > to about 30 or 40 a few times, but no longer stalls as before.

    What operating system do you have installed in your virtual machine
    and what filesystem are you using?  Is the backing zfs volume
    blocksize properly matched with the blocksize of the virtual machine's
    blocksize?  If the blocksize and offsets are not well matched, then
    performance would suffer quite a lot.

    The VM writes to the zfs volume would normally be synchronous writes
    (does not return util data is on disk), which will be slow unless you
    have added a zfs slog (perhaps with an SSD) to make synchronous writes
    faster.

    Bob
    --
    Bob Friesenhahn
    bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
    GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

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