[Drbd-dev] DRBD Trim/discard

[Drbd-dev] DRBD Trim/discard

[Eric Wheeler]

Hello all,


We would like to run DRBD backed by thin-provisioned volumes (think ZFS or 
dm-thinp) which require discard support to dereference unused block 
allocations.  (I searched around for DRBD trim/discard support with little 
commentary except the reference [1] below which does not apply to our use 
case.)


Is discard support on the roadmap?

What are the technical considerations for implementation?

I'm guessing this would be a relatively simple patch, just need to add a 
discard flag to the wire protocol and pass that to the backing device 
(after calculating the metadata offset, if any).

If you can comment on the desired implementation of such a feature and 
point me in the right direction I may be able to write a patch and test.

Any help you can offer would be greatly appreciated!

-Eric

[1] http://lists.linbit.com/pipermail/drbd-user/2012-March/017987.html


--
Eric Wheeler
eWheeler Inc.
http://www.globallinuxsecurity.pro/

Re: [Drbd-dev] DRBD Trim/discard

[Lars Ellenberg]

On Thu, Sep 26, 2013 at 12:01:40PM -0700, Eric Wheeler wrote:
> Hello all,
> 
> 
> We would like to run DRBD backed by thin-provisioned volumes (think
> ZFS or dm-thinp) which require discard support to dereference unused
> block allocations.  (I searched around for DRBD trim/discard support
> with little commentary except the reference [1] below which does not
> apply to our use case.)
> 
> 
> Is discard support on the roadmap?
> 
> What are the technical considerations for implementation?
> 
> I'm guessing this would be a relatively simple patch, just need to
> add a discard flag to the wire protocol and pass that to the backing
> device (after calculating the metadata offset, if any).
> 
> If you can comment on the desired implementation of such a feature
> and point me in the right direction I may be able to write a patch
> and test.
> 
> Any help you can offer would be greatly appreciated!

We are integrating DISCARD / TRIM support into our currently pending
DRBD 8.4.4 release, right now.
Code changes expected to be pushed with the RC2, latest early next week.

Thanks for testing and feedback,

Cheers,

	Lars

Re: [Drbd-dev] DRBD Trim/discard

[Eric Wheeler]

On Fri, 27 Sep 2013, Lars Ellenberg wrote:
> On Thu, Sep 26, 2013 at 12:01:40PM -0700, Eric Wheeler wrote:
>> We would like to run DRBD backed by thin-provisioned volumes (think
>> ZFS or dm-thinp) which require discard support to dereference unused
>> block allocations.
>
> We are integrating DISCARD / TRIM support into our currently pending 
> DRBD 8.4.4 release, right now. Code changes expected to be pushed with 
> the RC2, latest early next week.
>
> Thanks for testing and feedback,

I just sat down to look into TRIM support in the git tree, none of the 
commits in the shortlog are obvious. Has this already been committed? If 
so, do you have a commit number or alternate git tree that I can pull 
down?

-Eric

Re: [Drbd-dev] DRBD Trim/discard

[Lars Ellenberg]

On Thu, Oct 17, 2013 at 04:00:54PM -0700, Eric Wheeler wrote:
> 
> On Fri, 27 Sep 2013, Lars Ellenberg wrote:
> >On Thu, Sep 26, 2013 at 12:01:40PM -0700, Eric Wheeler wrote:
> >>We would like to run DRBD backed by thin-provisioned volumes (think
> >>ZFS or dm-thinp) which require discard support to dereference unused
> >>block allocations.
> >
> >We are integrating DISCARD / TRIM support into our currently
> >pending DRBD 8.4.4 release, right now. Code changes expected to be
> >pushed with the RC2, latest early next week.
> >
> >Thanks for testing and feedback,
> 
> I just sat down to look into TRIM support in the git tree, none of
> the commits in the shortlog are obvious. Has this already been
> committed? If so, do you have a commit number or alternate git tree
> that I can pull down?

You've been grepping for TRIM, I guess, where we used DISCARD ;-)

Look for "DISCARD" in the commit subjects.
I think it starts with
    drbd: prepare receiving side for REQ_DISCARD

Then a few more, and a few fixes for when exactly to expose QUEUE_FLAG_DISCARD.

Cheers,
	Lars