[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <571E667E.4080200@sandisk.com>
Date: Mon, 25 Apr 2016 11:48:30 -0700
From: Bart Van Assche <bart.vanassche@...disk.com>
To: Philipp Reisner <philipp.reisner@...bit.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 05/30] drbd: Introduce new disk config option
rs-discard-granularity
On 04/25/2016 09:42 AM, Philipp Reisner wrote:
> Am Montag, 25. April 2016, 08:35:26 schrieb Bart Van Assche:
>> On 04/25/2016 05:10 AM, Philipp Reisner wrote:
>>> As long as the value is 0 the feature is disabled. With setting
>>> it to a positive value, DRBD limits and aligns its resync requests
>>> to the rs-discard-granularity setting. If the sync source detects
>>> all zeros in such a block, the resync target discards the range
>>> on disk.
>>
>> Can you explain why rs-discard-granularity is configurable instead of
>> e.g. setting it to the least common multiple of the discard
>> granularities of the underlying block devices at both sides?
>
> we had this idea as well. It seems that real world devices like larger
> discards better than smaller discards. The other motivation was that
> a device mapper logical volume might change it on the fly...
> So we think it is best to delegate the decision on the discard chunk
> size to user space.
Hello Phil,
Are you aware that for aligned discard requests the discard granularity
does not affect the size of discard requests at all?
Regarding LVM volumes: if the discard granularity for such volumes can
change on the fly, shouldn't I/O be quiesced by the LVM kernel driver
before it changes the discard granularity? I think that increasing
discard granularity while I/O is in progress should be considered as a bug.
Bart.
Powered by blists - more mailing lists