linux-kernel - Re: 3.10: discard/trim support on md-raid1?

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Message-ID: <CAGqmV7qf14zrsimCMRsVWobq8SpLaavxPQvEyU6N=f1nBgvFHQ@mail.gmail.com>
Date:	Wed, 17 Jul 2013 00:44:15 +0400
From:	CoolCold <coolthecold@...il.com>
To:	NeilBrown <neilb@...e.de>
Cc:	Justin Piszcz <jpiszcz@...idpixels.com>,
	Linux kernel <linux-kernel@...r.kernel.org>,
	Linux RAID <linux-raid@...r.kernel.org>
Subject: Re: 3.10: discard/trim support on md-raid1?

Neil, I've tryed to look around commit logs but failed to find commit
where discard/trim were added.
I was looking via
http://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/log/drivers/md?id=9f2a940965286754f3a34d5737c3097c05db8725&qt=grep&q=discard+support
, tryed just "discard" without support - found commits about dm, not
md, though.

Can you shed some light here? Thanks in advance.

(resent in plaintext mode, please reply to this one)


On Tue, Jul 16, 2013 at 11:15 AM, NeilBrown <neilb@...e.de> wrote:
> On Sat, 13 Jul 2013 06:34:19 -0400 "Justin Piszcz" <jpiszcz@...idpixels.com>
> wrote:
>
>> Hello,
>>
>> Running 3.10 and I see the following for an md-raid1 of two SSDs:
>>
>> Checking /sys/block/md1/queue:
>> add_random: 0
>> discard_granularity: 512
>> discard_max_bytes: 2147450880
>> discard_zeroes_data: 0
>> hw_sector_size: 512
>> iostats: 0
>> logical_block_size: 512
>> max_hw_sectors_kb: 32767
>> max_integrity_segments: 0
>> max_sectors_kb: 512
>> max_segment_size: 65536
>> max_segments: 168
>> minimum_io_size: 512
>> nomerges: 0
>> nr_requests: 128
>> optimal_io_size: 0
>> physical_block_size: 512
>> read_ahead_kb: 8192
>> rotational: 1
>> rq_affinity: 0
>> scheduler: none
>> write_same_max_bytes: 0
>>
>> What should be seen:
>> rotational: 0
>
> What has "rotational" got to do with "supports discard"?
> There may be some correlation, but it isn't causal.
>
>> And possibly:
>> discard_zeroes_data: 1
>
> This should be set as the 'or' of the same value from component devices.  And
> does not enable or disable the use of discard.
>
> I don't think that "does this device support discard" appears in sysfs.
>
> I believe trim does work on md/raid1 if the underlying devices all support it.
>
> NeilBrown
>
>
>
>>
>> Can anyone confirm if there is a workaround to allow TRIM when using
>> md-raid1?
>>
>> Some related discussion here:
>> http://us.generation-nt.com/answer/md-rotational-attribute-help-206571222.ht
>> ml
>> http://www.progtown.com/topic343938-ssd-strange-itself-conducts.html
>>
>>
>> Justin.
>>
>>
>> --
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>



-- 
Best regards,
[COOLCOLD-RIPN]
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