From: NeilBrown <neilb@suse.de>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Shaohua Li <shli@kernel.org>,
linux-raid@vger.kernel.org, axboe@kernel.dk,
Shaohua Li <shli@fusionio.com>
Subject: Re: [RFC 1/2] MD: raid5 trim support
Date: Wed, 18 Apr 2012 06:26:41 +1000 [thread overview]
Message-ID: <20120418062641.000e881c@notabene.brown> (raw)
In-Reply-To: <CABE8wwswKWQ=LDbx0ysTaZf2Hz0jD_q45FNF0jw96ZwZdJiHPw@mail.gmail.com>
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On Tue, 17 Apr 2012 07:46:03 -0700 Dan Williams <dan.j.williams@intel.com>
wrote:
> On Tue, Apr 17, 2012 at 1:35 AM, Shaohua Li <shli@kernel.org> wrote:
> > Discard for raid4/5/6 has limitation. If discard request size is small, we do
> > discard for one disk, but we need calculate parity and write parity disk. To
> > correctly calculate parity, zero_after_discard must be guaranteed.
>
> I'm wondering if we could use the new bad blocks facility to mark
> discarded ranges so we don't necessarily need determinate data after
> discard.
>
> ...but I have not looked into it beyond that.
>
> --
> Dan
No.
The bad blocks framework can only store a limited number of bad ranges - 512
in the current implementation.
That would not be an acceptable restriction for discarded ranges.
You would need a bitmap of some sort if you wanted to record discarded
regions.
http://neil.brown.name/blog/20110216044002#5
NeilBrown
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next prev parent reply other threads:[~2012-04-17 20:26 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-17 8:35 [RFC 0/2] raid5 trim support Shaohua Li
2012-04-17 8:35 ` [RFC 1/2] MD: " Shaohua Li
2012-04-17 14:46 ` Dan Williams
2012-04-17 15:07 ` Shaohua Li
2012-04-17 18:16 ` Dan Williams
2012-04-17 20:26 ` NeilBrown [this message]
2012-04-18 0:58 ` Shaohua Li
2012-04-18 4:48 ` NeilBrown
2012-04-18 5:30 ` Shaohua Li
2012-04-18 5:57 ` NeilBrown
2012-04-18 6:34 ` Shaohua Li
2012-04-25 3:43 ` Shaohua Li
2012-05-08 10:16 ` Shaohua Li
2012-05-08 15:52 ` Dan Williams
2012-05-09 3:12 ` Shaohua Li
2012-05-08 20:17 ` NeilBrown
2012-04-17 8:35 ` [RFC 2/2] MD: raid5 avoid unnecessary zero page for trim Shaohua Li
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