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SubjectRe: XFS and journalling filesystems
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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