Messages in this thread |  | | From | "Stephen C. Tweedie" <> | | Date | Tue, 1 Jun 1999 00:10:41 +0100 (BST) | | Subject | Re: XFS and journalling filesystems |
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Hi,
On Fri, 28 May 1999 10:11:02 -0600, "Jeff Merkey" <jmerkey@timpanogas.com> said:
> NTFS, for example, only posts meta data to the log file for restart, > and does not post user writes to the journal. This means you can > lose user data on a restart.
This is expected behaviour. This is the defined Unix semantics. Unix provides an API which allows the application to request data synchronisation with the disk if it wants it --- the semantics explicitly do not guarantee this unless you use fsync/fdatasync or O_SYNC/O_DSYNC.
> If XFS is only writing meta data to the journal, and not user data, > as you suggest, then you are technically correct that reads do not > have to be serialized, however, this also means that XFS is not a > **TRUE** journalling file system because you can lose user data on > restarts
Of course it is true journaling. It just has different semantics to a system which journals data synchronously.
> and the benefits it provides for journalling are not much better > than running "fsck" after a system crash.
That is the whole point, tho. fsck elimination is precisely why most Unix journaling filesystems were written.
> Surely this is not the case -- this would mean that XFS is no better than > NTFS.
Huh?
--Stephen
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