[dm-devel] [lvm-devel] dm thin: optimize away writing all zeroes to unprovisioned blocks

[Eric Wheeler]

On Fri, 5 Dec 2014, Mike Snitzer wrote:

> On Thu, Dec 04 2014 at 10:33am -0500,
> Mike Snitzer <snitzer at redhat.com> wrote:
> In testing this patch it is now quite clear that this change seriously
> impacts test coverage in the device-mapper-test-suite because dmts'
> wipe_device() uses /dev/zero as the ifile for dd to write to the disk.
> As such, with this patch all tests expecting to see provisioned blocks
> as a side-effect of wipe_device now fail (e.g. DiscardQuickTests).
>
> So this change won't go upstream until full test coverage can be
> restored in dmts.  I'll see what I can come up with but it is low
> priority.

Can dtms use /dev/urandom?

> BTW, this also makes me wonder if this change will be extremely
> unintuitive to existing or future user of DM thinp.  So much so that it
> might be best to require a new thin-pool feature flag to enable this
> optimization.

Good idea, some may wish to turn it off.  IMO, leaving it on by default 
would likely work for most use cases.

-Eric

> Mike
>
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