linux-ext4 - Re: Feature request: e2fsck -z

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Message-ID: <4E422686.8080207@gmail.com>
Date:	Wed, 10 Aug 2011 07:34:46 +0100
From:	Ric Wheeler <ricwheeler@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	linux-ext4@...r.kernel.org
Subject: Re: Feature request: e2fsck -z

On 08/09/2011 06:52 PM, H. Peter Anvin wrote:
> Hi all,
>
> This is something I've wanted to see for a very long time, and it
> finally occurred to me that perhaps I should say something about it!
>
> It would be a very nice thing to have a flag to e2fsck, presumably -z,
> to zero out any unused data blocks, inodes and so on.  The goal is to
> minimize the amount of space required after compressing a virtual disk
> image or similar, and to make sure any non-data isn't lying around.
>
> 	-hpa
>

Do you need it to be in the fsck tool?

If you have a sparsely allocated block map under your file system, doing a zero 
of all blocks could add hours for a big, slow S-ATA drives (2-3 hours for a 1TB 
drive).

An alternative for SSD's and devices that do TRIM/UNMAP would be to use one of 
the batched discard tools (that would make discarded data read back as zeroed).

Thanks!

Ric

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