Questions regarding journal replay

Ralf Hildebrandt Ralf.Hildebrandt at
Fri Feb 27 16:40:41 UTC 2009

* Theodore Tso <tytso at>:
> On Wed, Feb 25, 2009 at 08:02:15PM +0100, Ralf Hildebrandt wrote:
> > > 
> > > Did you find some documentation that actually recommend that large of
> > > an external journal?
> > 
> > It says the "journal has a  maximum size of 128M"
> That's clearly not right.  Where did you see that?  We should make
> sure it gets fixed...

The journal options in the tune2fs man page say:

****** CITE *********


Create a journal stored in the filesystem of size journal-size megabytes.
The size of the journal must be at least 1024 filesystem blocks (i.e.,
1MB if using 1k blocks, 4MB if using 4k blocks, etc.) and may be no more
than 102,400 filesystem blocks.  There must be enough free space in the
filesystem to create a journal of that size.


Attach the filesystem to the journal block device located on
external-journal.  The external journal must have been already created
using the command

  mke2fs -O journal_dev external-journal
Note that external-journal must be formatted with the same block size as
filesystems which will be using it.  In addition, while there is support
for attaching multiple filesystems to a single external journal, the
Linux kernel and e2fsck(8) do not currently support shared exter‐ nal
journals yet.

****** CITE *********

It would be nice if the manpage included a sentence like:

If an external journal is used, the whole journal block device will be
used as journal.

The sentence "... be no more than 102,400 filesystem blocks." gives the
impression (to me, that is) that the same restrcition applies to an
external-journal as well!

Yes, I know *NOW* that's not the case.

Ralf Hildebrandt                                Ralf.Hildebrandt at
Charite - Universitätsmedizin Berlin            Tel.  +49 (0)30-450 570-155
Geschäftsbereich IT | Abt. Netzwerk             Fax.  +49 (0)30-450 570-962
Hindenburgdamm 30 | 12200 Berlin

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