linux-kernel - Re: [Drbd-dev] [PATCH 04/30] drbd: Implement handling of thinly provisioned storage on resync target nodes

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Date:	Mon, 25 Apr 2016 11:21:13 -0500
From:	Philipp Reisner <philipp.reisner@...bit.com>
To:	Bart Van Assche <bart.vanassche@...disk.com>
Cc:	Jens Axboe <axboe@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"drbd-dev@...ts.linbit.com" <drbd-dev@...ts.linbit.com>
Subject: Re: [Drbd-dev] [PATCH 04/30] drbd: Implement handling of thinly provisioned storage on resync target nodes

Am Montag, 25. April 2016, 08:28:45 schrieb Bart Van Assche:
> On 04/25/2016 05:10 AM, Philipp Reisner wrote:
> > If during resync we read only zeroes for a range of sectors assume
> > that these secotors can be discarded on the sync target node.
> 
> Hello Phil,
> 
> With which interconnect(s) has this patch been tested? I'm afraid that
> for high-speed interconnects this patch will slow down I/O instead of
> making it faster because all_zero() examines all data before it is sent.
> 

Hi Bart,

that it might make things slower is true for sure. The benefit it
provides is to de-allocate blocks on the secondary obviously.
The whole feature is optional and it is off by default.

Obviously we want to have a generic interface like SEEK_HOLE/
SEEK_DATA for block devices, but that does not exist as of today.

best regards,
 Phil