QEMU's default qcow2 L2 cache size is too small for large images (and small
cluster sizes), resulting in very bad performance.
shows huge performance hit for a 20GB qcow2 with default 64kB cluster size:
L2 Cache, MiB Average IOPS
1 (default) 5100
The above link also gives the formula:
optimal L2 cache size = L2 table size = (8 Byte) * (disk size) / (cluster size)
and the QEMU command line for setting L2 cache size, which is not persistent,
but must be specified at each invocation:
qemu-system-x86_64 -drive file=hd.qcow2,l2-cache-size=2621440
I'd like to set the l2-cache-size in libvirt xml, but cannot make out how to do
There are only hints in the comments at the above link and at
and an earlier unanswered question on this list
Has anyone successfully done this, and could you please give an example of the
actual libvirt xml used?
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