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Re: [Q] e2image: tools for sparse files & e2sfck support



On Wed, Jan 08, 2003 at 01:08:04PM +0100, Gregor Zattler wrote:
> i have two twofold e2image related questions:
> 
> 1)  The man page mentions "cp (1)"'s --sparse=always option.  I
>     wonder if there are sparse aware tools which
> 
>     a) display the "real" amount of disk space occupied by a
>        sparse file

ls -s will return the amount of "real" disk space occupied by a sparse
file.

>     b) compress sparse files (other than compressing very
>        thightly several GiB of zeros)

bzip2 or gzip do a very nice job of compressing a sparse file.
Unfortunately, bunzip2 and gunzip do not write out a sparse file when
it uncompresses it.  It isn't hard to write a program though that will
write a sparse file given a file with lots of zeros on stdin, which
you could use as follows:

	bunzip2 < foo.img.bz2 | make-sparse foo.img

Writing such a program is left as an exercise to the reader.  If
someone writes one and sends it to me, I'll likely even include it in
e2fsprogs.  :-)

> 2)  "E2fsck, mke2fs, etc. will now reliably notice when image
>     files are mounted using the loopback interface.  (Addresses
>     Sourceforge bug #619119)" (quoted from RELEASE-NOTES.gz)
> 
>     a) Is e2fsck now able to use (raw) e2images while repairing ext2
>        file systems?

You can run e2fsck on a raw e2image; e2image -r makes a raw image
which contains all the blocks that e2fsck would ever try to look at.
I will often ask for a bzip2 compressed raw image file when trying to
debug some problem with a filesystem, and I will often run e2fsck
against the raw image to see how e2fsck is complaining about a
particular filesystem.

However, while you could allow e2fsck to "fix" the problems it finds
in the raw e2image, this wouldn't actually help you fix the problem
found in the original filesystem.  

>     b) Is this also useful for ext3 file systems?

See above.

						- Ted





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