From: Andi Kleen <andi@firstfloor.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>, xfs@oss.sgi.com
Subject: Re: [PATCH] mkfs: add discard support
Date: Wed, 07 Oct 2009 22:24:07 +0200 [thread overview]
Message-ID: <87iqerymu0.fsf@basil.nowhere.org> (raw)
In-Reply-To: <20091007044215.GK9464@discord.disaster> (Dave Chinner's message of "Wed, 7 Oct 2009 15:42:16 +1100")
Dave Chinner <david@fromorbit.com> writes:
> On Tue, Oct 06, 2009 at 02:47:58PM -0400, Christoph Hellwig wrote:
>> Call the BLKDISCARD ioctl to mark the whole disk as unused before creating
>> a new filesystem. This will allow SSDs, Arrays with thin provisioning support
>> and virtual machines to make smarter allocation decisions.
>
> Good idea, but perhaps the discard should be optional rather than
> unconditional. My immediate thought was the SOP for setting up
> encrypted devices - fill the empty disk with random data before
> setting up the encrypted device. If you then send it a discard....
This actually doesn't really work for SSDs, because SSDs typically
have more internal capacity than they advertise and when you fill
it up then it will just allocate new blocks and leave some of the
blocks with the existing data around.
AFAIK there's no way to really reliably delete something physically
on a SSD short of applying a hammer.
For thin provisioning arrays you have similar problems.
So I think Christoph's case of making it default is fine.
-Andi
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next prev parent reply other threads:[~2009-10-07 20:22 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-06 18:47 [PATCH] mkfs: add discard support Christoph Hellwig
2009-10-07 4:42 ` Dave Chinner
2009-10-07 6:05 ` Michael Monnerie
2009-10-07 14:11 ` Christoph Hellwig
2009-10-07 20:24 ` Andi Kleen [this message]
2009-10-09 2:30 ` Dave Chinner
2009-10-10 4:22 ` Andi Kleen
2009-10-10 16:24 ` Christoph Hellwig
2009-10-12 1:33 ` Andi Kleen
2009-10-07 22:26 ` [PATCH v2] " Christoph Hellwig
2009-10-10 20:55 ` Eric Sandeen
[not found] <1235789111.21721254856913943.JavaMail.root@mail-au.aconex.com>
2009-10-06 19:24 ` [PATCH] " Nathan Scott
2009-10-06 19:26 ` Christoph Hellwig
2009-10-07 1:18 ` Christoph Hellwig
2009-10-07 1:20 ` Nathan Scott
2009-10-07 3:55 ` Eric Sandeen
2009-11-12 16:04 ` Christoph Hellwig
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