On 16.06.2011 07:10, Kazuya Mio wrote:
2011/06/16 5:31, Tomasz Chmielewski wrote:
Out of curiosity: is there a minimal kernel version requirement (one
which can be safely used with e4defrag)?
EXT4_IOC_MOVE_EXT ioctl was merged 2.6.31. And then some bugfix were merged
before 2.6.35. I suggest you to build 2.6.35 or later if you try to do
e4defrag.
e4defrag also merged some bugfix like this patch, so you should use
the latest e4defrag.
Thanks for clarification.
If you find out something about online defrag, please post a comment.
My main usage for e4defrag would be defragmenting virtual guest (like
KVM) file-based images.
These images are typically quite small when created (i.e. qcow2, or a
"raw", sparse file), but grow in time, which leads to serious fragmentation.
I noticed that when using e4defrag on such a file-based image, while the
guest is running (i.e. the file is in use), all IO from that guest to
the disk (disk is this file) is "frozen".
In other words, as soon as we run e4defrag, any guest writes to that
file will only complete if e4defrag finishes. As the images can be quite
big, it can mean guest IO can be frozen even for hours.
Is it a known/intended limitation (at least, it behaved like this when I
tried e4defrag a few months ago)?
In some cases, it can be a serious drawback, potentially leading to
filesystem corruption in the guest - if guest block layer is SCSI, with
default settings (at least in Linux) it may detect that no IO happened
for some time, and just "offline" the disk.
--
Tomasz Chmielewski
http://wpkg.org
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