[Users] Maximum JFS file (not filesystem) size with the 2.6.27
openvz patched kernel
Scott Dowdle
dowdle at montanalinux.org
Tue Sep 8 05:41:52 EDT 2009
Dwight,
According to the wikipedia file system comparison page (http://en.wikipedia.org/wiki/Comparison_of_file_systems), JFS has a maximum file size of 4 PiB.
----- "Dwight Schauer" <dschauer at gmail.com> wrote:
> Hello fellow OpenVZers,
>
> This is not really and OpenVZ situation perse, but an openvz patched
> kernel was involved.
>
> I tarred up a couple filesystems and piped the tar stream through ssh
> to a remote computer (hardware node running the OpenVZ patched 2.6.27
> kernel) where I dd'ed it to a file. This a common backup method I've
> been using for a few years now if I'm going to wipe a system and
> start
> over.
>
> I'm using JFS on the arch linux based hardware node that was being
> copied to.
>
> The resulting file ended up being 137G (which is about right based on
> the source filesystem usage).
>
> du --human --total a4b4.tar
> 137G a4b4.tar
> 137G total
>
> However, I can only restore from 63G of the tar ball, so I attempted
> to see how much could be read.
>
> dd if=a4b4.tar of=/dev/null
> dd: reading `a4b4.tar': Input/output error
> 123166576+0 records in
> 123166576+0 records out
> 63061286912 bytes (63 GB) copied, 1193.69 s, 52.8 MB/s
>
> There were no critical files in that tar ball that are not kept
> elsewhere, that is not the issue. At this point I can consider what
> is
> past the 63G point in the tarball to unrecoverable, which is fine.
>
> I tried skipping the first 63GB, but that does not work.
>
> dd if=a4b4.tar skip=123166576 of=/dev/null
> dd: reading `a4b4.tar': Input/output error
> 0+0 records in
> 0+0 records out
> 0 bytes (0 B) copied, 27.2438 s, 0.0 kB/s
>
> It seems like it took a while to figure out that it could not perform
> this operation.
>
> Yeah, I know, I could have used bzip and made 2 separate files, I
> could have used rsync -av, I could have checked tarball before wiping
> the source files systems, etc, that is not the point here. Now that I
> know that JFS on my setup has a 63GB file size limit, I know now to
> accommodate for that in the future.
>
> I'm mainly just curious on how the system could write a larger file
> than it can read.
>
> Dwight
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--
Scott Dowdle
704 Church Street
Belgrade, MT 59714
(406)388-0827 [home]
(406)994-3931 [work]
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