On 08/10/2011 09:16 AM, Andreas Dilger wrote:
On 2011-08-10, at 12:34 AM, Ric Wheeler wrote:
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.
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).
I think Ted has a tool that does this already. It should be relatively simple oo do, like "dd if=/dev/zero of=/mountpoint/temp_zero_file&& rm /mountpoint/temp_zero_file.
This will work but will be a potential multi-hour long process (and cause out of
space errors at some point for other applications for a very brief window :))
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).
In fact, I thought Lukas has already made a tool for sending BLKDISCARD for all unused parts of the filesystem?
Cheers, Andreas
Right, I think he has. That tool (not part of fsck) would do the job much
quicker for enabled devices,
Ric
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