I will read the suggested white papers as I have time (swamped right now,
getting the NetWare FS (FENRIS) ready for open source next Tuesday,
hopefully it may be helpful to all, including you guys -- we are putting ALL
of it under the GPL (less the NT specific IFS code which is about 18,000
lines oddly enough)). Sounds like the term "journalling" is like the term
"clustering" from an industry perspective, and some FS's aren't really
journalled, but reapply this term for marketing positioning. XFS appears to
be more similar to NTFS than I had previously thought.
There is still obvious benefits to including the XFS level of capability
into Linux, even though it's not really a journalling file system. A log
based file system that logs user writes and allows rollbacks is what most
folks assume when the term "journalling" is used. I think this may have
been what folks were assuming. I understand better now what you are doing
now and what XFS actually provides.
Jeff
----- Original Message -----
From: Jim Mostek <mostek@sgi.com>
To: Jeff Merkey <jmerkey@timpanogas.com>
Cc: <mostek@sgi.com>; <andreas@andreas.org>; <mcai7et2@stud.umist.ac.uk>;
<linux-kernel@vger.rutgers.edu>
Sent: Friday, May 28, 1999 10:53 AM
Subject: Re: XFS and journalling filesystems
>
> Jeff,
>
> XFS does not put data into the log. It keeps track of meta-data operations
> in the log. One goal of XFS is to remove the need for fsck at start-up.
> This is a very big deal when one has very large file systems. fsck can
> take a very long time on very large file systems.
>
> If you are looking for a file system that logs data, XFS is
> not your solution. XFS does allow a file to be written synchronously
> with O_SYNC so you can guarantee that the data is on disk
> when the write returns.
>
> There is much more to XFS than the log and journalling.
> Saying that because XFS doesn't log data, it is no better than NTFS
> doesn't address all the other aspects of XFS.
>
> Have you seen the latest XFS white paper? The current one off of SGI's
> web page is pretty old. The latest paper compares NTFS, XFS,
> VxFS and is a pretty good overview of XFS. XFS has had more
> stuff added to it in recent months (like a new defag tool)
> which is not in the paper.
>
> I just looked around and I don't see a publicly available web
> jumper for it. We'll set one up and I'll send it around next
> week.
>
> Jim
>
> >
> >
> >Jim,
> >
> >Some journal based FS's will serialize reads when A) there is cached data
> >(in a buffer cache for example), and there is a requirement for writes to
be
> >committed real time with reads always having the most current data, and
B)
> >when transactioning is implemented above the FS and you have writes and
> >reads to the same block (do you return the stale data, or do you return
the
> >write that was posted to the journal and cached, but not yet committed?)
In
> >theory, you could avoid serializing on reads, but you may get stale data.
> >
> >This applies to journalled FS's that post both user data and meta data to
> >the log file. 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. 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, and the benefits it provides for journalling are not much
better
> >than running "fsck" after a system crash.
> >
> >Surely this is not the case -- this would mean that XFS is no better than
> >NTFS.
> >
> >Jeff
> >
> >----- Original Message -----
> >From: Jim Mostek <mostek@sgi.com>
> >To: Andreas Bogk <andreas@andreas.org>
> >Cc: <jmerkey@timpanogas.com>; <mcai7et2@stud.umist.ac.uk>;
> ><linux-kernel@vger.rutgers.edu>
> >Sent: Friday, May 28, 1999 8:58 AM
> >Subject: Re: XFS and journalling filesystems
> >
> >
> >> >feature for video: guaranteed bandwidth. Also, journalling slows down
> >> >reading, but speeds up writing, which is again important for
> >> >video. So, as long as ext3 is not there, I'll be very happy about XFS.
> >>
> >> How does journalling slow down reading? The only time XFS needs
> >> to create a transaction is when changing meta-data (like a create,
> >> file extend, remove, ...).
> >> XFS doesn't do transactions for time updates. Do other FSs?
> >> XFS doesn't do transactions on writting if the file is already
> >> allocated.
> >>
> >> Jim
> >>
> >> >
> >> >Andreas
> >> >
> >> >--
> >> >Reality is two's complement. See:
> >> >ftp://ftp.netcom.com/pub/hb/hbaker/hakmem/hacks.html#item154
> >> >
> >> >-
> >> >To unsubscribe from this list: send the line "unsubscribe
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> >in
> >> >the body of a message to majordomo@vger.rutgers.edu
> >> >Please read the FAQ at http://www.tux.org/lkml/
> >> >
> >>
> >>
> >
>
>
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