[dm-devel] thinp zeroing
Mike Snitzer
snitzer at redhat.com
Thu Feb 23 02:49:18 UTC 2012
Nice write-up. It is concerning that we have to go to such lengths but
I don't see a way around it without limiting who can consume thinp.
On Wed, Feb 22 2012 at 9:14am -0500,
Joe Thornber <thornber at redhat.com> wrote:
> ** Discards
>
> DISCARDs *must* result in data being zeroed. Some devices set the
> discard_zeroes_data flag. This is not good enough; you cannot use
> this flag as a guarantee that the data no longer exists on the
> disk. So real zeroing must occur. I suggest we write a separate
> target that zeroes data just before discarding it, and stack it
> under the thin-pool. The performance impact of this will be
> significant; to the point that we may wish to turn discard within
> the fs off; instead doing periodic tidy-ups.
...
> ** Summary of work items [0/5]
>
> - [ ] Implement the discard-really-zeroes target [1 month]
I don't think it'll take a month. Probably a focused week to 2 weeks.
I can develop this target before jumping in to the HSM target (unless
you'd rather I start in on HSM asap).
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