Hello Antonio-
First, thank you for the wonderful tool. I've used ddrescue many times
to recover data from failing hard drives, as well as for manually
imaging working drives (the progress/speed display is very nice).
I'm curious whether it's possible for ddrescue to preallocate space for
the file that it writes using posix_fallocate. I don't envision this as
standard behavior; I remember reading a message that you posted to the
mailing list saying that on some platforms, the size information is not
available at all. Additionally, I've seen failing hard drives report
erroneous sizes (such as an 80GB drive showing as 2.1TB -- it apparently
reported 0xFFFFFFFF when queried).
If the size is available (which would be a compile-time option) and
correct (which would be a runtime option that defaults to false), would
you support using a preallocation system call in order to improve
filesystem performance and reduce fragmentation? Modern filesystems such
as ext4, xfs, ocfs2, etc. support very efficient preallocation of large
files and it seems worth it to take advantage of this capability.
I did a quick grep through the source code and didn't find any instance
of 'allocate'. My understanding (which is not all that likely to be
correct) is that this behavior is distinct from the --sparse option. A
sparse file's size is reported to be much larger than the allocated size
on disk, whereas the new behavior would tell the filesystem in advance
that e.g. the image file will eventually contain 250GB. The filesystem
will then allocate this space as contiguously as possible.
Semi-related question: is there a publicly accessible source code
repository for ddrescue? I created a repository on GitHub (
http://github.com/mruffalo/ddrescue ) that I will use to publish my
changes in the event that I implement this feature myself. It contains
all released versions of ddrescue back to version 0.6 and the authorship
timestamps match the modification times of the archives on the GNU
mirrors. For example:
Author: Antonio Diaz Diaz <[email protected]> 2005-01-04 05:39:00
Committer: Matthew Ruffalo <[email protected]> 2010-05-30 14:16:34
Tags: v0.9
Thank you,
--
Matt Ruffalo...
Department of Electrical Engineering and Computer Science
Case Western Reserve University
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