Messages in this thread | | | Date | Mon, 27 Mar 2000 20:47:14 -0800 | From | ncm@nospam ... | Subject | Is ReiserFS really a journaling file system, or is it really just a synchronous-metadata file system like BSD FFS? |
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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?
Nathan Myers ncm@nospam.cantrip.org
p.s. I know ReiserFS has all kinds of cool semantics in addition to traditional file-system stuff; I'm just asking about its recovery characteristics.
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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