> I am sorry to ask problem. What are realtime extents and for what?
> As this message is probably not-quite-on-topic for this list I will keep
> this brief, and welcome any responses either to the list or through
> private email.
> We're interested in using XFS as the file system on an embedded device.
> This device performs data logging tasks. Data integrity is important,
> and the device could potentially be used in an environment where power
> failures happen regularly. After a power failure, the device must
> recover very quickly -- this is why XFS looks like good solution to our
> I'd like some information on how data is written to the disk -- what is
> written to the disk and what is stored in the journal, at what stages
> the structures on the disk are updated, how the filesystem recovers
> after an unclean shutdown, and so on. If a file is damaged by unclean
> shutdown, then subsequently recovered, what state will the file be in?
> What kind of corruption, if any, could it suffer?
In XFS only meta-data is journaled, typically high-performance
applications using XFS use "direct" I/O to "pre-allocated" files, thus
eliminating loss of buffered data, and keeping meta-data ops
(i.e. allocations/extensions) to a minimum, whilst running the
disks at hardware speed.
> Richard Downer * Telecom Network Test Division * Agilent Technologies
First would be to scan the design docs & white papers available at:
Look on the left for the "Design", "1999 XFS White Paper", &
"Usenix Paper" links.
Some of the material is old, but provides the basis for the
Also check out the "Selected original 1993 XFS design documents"
link near the bottom of the page..
After that, or, if that's already been done, try us again..