ncm@nospam.cantrip.org wrote:
>
> I have seen the ReiserFS described as a "journaling filesystem", but
> in examining the project web page, it appears not to be. In fact, I
> see described there a "journaling patch" which seems to journal FS
> metadata, but not file contents. In particular:
>
> This is metadata logging only. If you hit the reset button in the
> middle of a kernel compile, you will end up with a bunch of
> invalid .o files, but the directory tree will remain valid. If
> you run sync a few times and then hit the reset button, data and
> metadata will both be valid.
>
> http://devlinux.com/projects/reiserfs/jrnl/
>
> As I understand it, a journaling file system is one in which, if you
> pull the plug at any point, all the metadata _and_ file data accurately
> reflect a recoverable self-consistent state at a some instant. IIUC,
> it is what is promised by Veritas and the IBM and SGI systems which are
> being groomed for inclusion. Not to journal file contents somewhere
> seems to make such semantics impossible.
>
> Is it that the file system layout itself supports journaling, but
> that the VFS layer doesn't support the semantics needed really to
> get it?
>
> (This also begs the question, if terminology is so abused here, is ext3
> really a journaling fs? (And, is ext2 a "journaling fs" just because
> the ext3 patch exists?))
>
> I hope my impression is wrong, and that in fact all these file systems
> provide similar recovery semantics. Can someone answer authoritatively?
There are different levels of journaling. Most FS journaling only journals the metadata.
Both ext3 (in current versions) and reiserfs do this. At some point the reiserfs team may
add options to mkfs to allow full journaling. This would hurt perf but may be necessary
if you are using the FS as a DB.
Ed Tomlinson <tomlins@cam.org>
>
> p.p.s. Sorry about the title, it was my impression that all
> ReiserFS-related postings have to have long titles. :-)
>
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