• aliguori's avatar
    Use writeback caching by default with qcow2 · 4dc822d7
    aliguori authored
    qcow2 writes a cluster reference count on every cluster update.  This causes
    performance to crater when using anything but cache=writeback.  This is most
    noticeable when using savevm.  Right now, qcow2 isn't a reliable format
    regardless of the type of cache your using because metadata is not updated in
    the correct order.  Considering this, I think it's somewhat reasonable to use
    writeback caching by default with qcow2 files.
    It at least avoids the massive performance regression for users until we sort
    out the issues in qcow2. 
    Signed-off-by: default avatarAnthony Liguori <aliguori@us.ibm.com>
    git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5879 c046a42c-6fe2-441c-8c8c-71466251a162
block-qcow2.c 80.9 KB