* How defragmentation works in linux filesystems ?
@ 2013-01-07 9:27 Sankar P
2013-01-15 21:23 ` Phillip Susi
0 siblings, 1 reply; 2+ messages in thread
From: Sankar P @ 2013-01-07 9:27 UTC (permalink / raw)
To: Kernelnewbies, linux-fsdevel
Hi,
Is there any technical article explaining how defragmentation works in
linux filesystems, say btrfs or ext4 ?
Do they recreate the file data blocks and change the root pointer to
the new extent ? Or do they do some kind of moving blocks around ? Or
is it based on some other strategy ? Partial defragmentation (based on
either byte offset or extents) is also supported by any of the file
systems ?
Is there a standard way to trigger a defragmentation operation (an
ioctl ?) that my filesystem could implement so that any user space
tool that work with other fs will work with mine too ? (Like, how
FIEBMAP ioctl can help in giving the extent information for a file
from the userspace)
I googled a bit to find any articles explaining this. But could not
get anything the design. So links to any documentation, article
explaining the linux filesystems' way of defragmenting are welcome.
Thanks.
--
Sankar P
http://psankar.blogspot.com
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: How defragmentation works in linux filesystems ?
2013-01-07 9:27 How defragmentation works in linux filesystems ? Sankar P
@ 2013-01-15 21:23 ` Phillip Susi
0 siblings, 0 replies; 2+ messages in thread
From: Phillip Susi @ 2013-01-15 21:23 UTC (permalink / raw)
To: Sankar P; +Cc: Kernelnewbies, linux-fsdevel
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
On 1/7/2013 4:27 AM, Sankar P wrote:
> Hi,
>
> Is there any technical article explaining how defragmentation works
> in linux filesystems, say btrfs or ext4 ?
>
> Do they recreate the file data blocks and change the root pointer
> to the new extent ? Or do they do some kind of moving blocks around
> ? Or is it based on some other strategy ? Partial defragmentation
> (based on either byte offset or extents) is also supported by any
> of the file systems ?
e4defrag uses an ioctl to allocate a new donor inode with enough
contiguous blocks to hold the original, then atomically copy the
blocks and swap the pointers.
> Is there a standard way to trigger a defragmentation operation (an
> ioctl ?) that my filesystem could implement so that any user space
> tool that work with other fs will work with mine too ? (Like, how
> FIEBMAP ioctl can help in giving the extent information for a file
> from the userspace)
No.
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