Libguestfs - Nov 2015 - RFE: 'fstrim' minimum block size when sparsifying qcow2 should be 64K

As the minimum block size to discard in qcow2 is 64K, any point in
fstrimming smaller contiguous blocks?

TIA,
Y.

On Thu, Nov 05, 2015 at 01:10:54PM +0200, Yaniv Kaul
wrote:
> As the minimum block size to discard in qcow2 is 64K, any point in
> fstrimming smaller contiguous blocks?
For virt-sparsify we just use the default that the util-linux
'fstrim -m' option uses, which (according to the fstrim manual) is 0
so it will try to discard any contiguous extent.

Unfortunately it's hard to tell what the best minimum free extent
would be.  The disk image might not be qcow2 -- if it was raw then any
4K or even 1K block could be worth freeing.

Is it a lot slower if we use a smaller minimum free extent?

Rich.

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