[lug] Convertion of ext4 Sparse Files

[stimits at comcast.net]

----- Original Message -----From: stimits at comcast.netTo: Lee Woodworth <blug-mail at duboulder.com>Sent: Fri, 05 Jan 2018 23:06:22 -0000 (UTC)Subject: Re: [lug] Convertion of ext4 Sparse Files

This apparently only copies bytes directly into the start of the pre-created file and does not actually extract this as the original partition. If I try to loopback mount it this fails in the same way as trying to loopback mount a non-file system binary file. This is another case of dd not realizing it should consider the original a sparse file.
 
----- Original Message -----From: Lee Woodworth <blug-mail at duboulder.com>To: stimits at comcast.netSent: Fri, 05 Jan 2018 22:55:49 -0000 (UTC)Subject: Re: [lug] Convertion of ext4 Sparse Files

What happens if you preallocate the destination with dd if=/dev/zero of=... bs=... count=...and dd with if=src of=dest conv=nocreat,notrunc

On 01/05/2018 03:48 PM, stimits at comcast.net wrote:> Unfortunately this does not work (currently testing on Fedora 27), at least not for this file which was originally a dd of a GPT partition and then converted to sparse at a later time. Output and input files are both the sparse file size.> > It may be a matter of dd or other tools not detecting this as sparse for whatever reason, but I keep running into options for creating sparse files and not the reverse, e.g., dd has "conv=sparse", but not the reverse, so I can't force it to do a sparse to non-sparse conversion.> > ----- Original Message -----From: Will <will.sterling at gmail.com>To: Boulder (Colorado) Linux Users Group -- General Mailing List <lug at lug.boulder.co.us>Sent: Fri, 05 Jan 2018 22:09:51 -0000 (UTC)Subject: Re: [lug] Convertion of ext4 Sparse Files> > dd if=/path/sparse_file of=/path/nonsparse_file> > On Fri, Jan 5, 2018 at 2:55 PM, <stimits at comcast.net> wrote:> > Hi,> > I've been looking all over and am stumped. Files can be "sparse" where space isn't allocated until needed, and it is easy to create a sparse file. What I'm wondering...and am stumped about...there must be a way to take an image and convert it back to non-sparse...but how?> > cp with "--sparse=never" does not work (I'm trying on Fedora 23 through 27, plus Ubuntu 16.04). This may be a property of the file in question though...some people will have a large file with content such as text...this is an embedded system dd of a partition...it is a binary image containing an ext4 partition which can be copied via dd back onto other embedded systems...but this was converted to sparse format to save space. Is there a way to take such an image and put it back to its original size without the sparse attribute?> > Thanks!> _______________________________________________> > Web Page: http://lug.boulder.co.us> > Mailing List: http://lists.lug.boulder.co.us/mailman/listinfo/lug> > Join us on IRC: irc.hackingsociety.org port=6667 channel=#hackingsociety> > > > > > > _______________________________________________> Web Page: http://lug.boulder.co.us> Mailing List: http://lists.lug.boulder.co.us/mailman/listinfo/lug> Join us on IRC: irc.hackingsociety.org port=6667 channel=#hackingsociety>


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