Thanks Chris for the information, I've tried to answer your questions below
(and add some more)
> I'm new to XFS and researching the use of XFS as the filesystem for
> an application that writes sequential data streamed from gigabit
> Ethernet. This data is then read at the fastest possible throughput
> for further processing.
How much data are we talking about and how long before it's read?
(ie. can this fit in memory).
It will run between 1 - 5 hrs so will not fit in memory. At the moment the
disk subsystem will likely be RAID5 or RAID0
> Is there a way to increased the buffered i/o for a file to be larger
> than 64K (XFS_IOC_SETBIOSIZE in man xfs(5)) or would this have
> minimal effect on read/write performance?
Check the mount option "biosize".
I did and I believe the max is 2^16 bytes. Would this be beneficial if this
can be theoretically increased?
> Is buffered i/o part of the delayed allocation that I have read from
> other sources?
No.
Okay, Is there any valid documentation or user variables to control how
delayed allocation works?
> If I know the size of the data before receiving it, should I use the
> XFS_IOC_RESVSP64 (man xfs(5)) in the application with unwritten=0
> option set for the filesystem?
XFS_IOC_RESVSP64 probably won't hurt (sometimes it's *really* handy
but it depends). unwritten=0 for the fs I doubt will make much
difference (not to mention the fact it probably doesn't do what you
think it does).
I mentioned unwritten=0 because from the man pages it seems that it is not
the default setting and when unwritten=1, the writing performance of
XFS_IOC_RESVSP64 would drop rather than improve.
> Using this technique, would it be reasonable to assume the XFS
> overhead is low enough for the throughput to be near the hardware
> benchmarks (sustained read/write)?
40MB/s? Easily I should think.
For streaming data it's more of an issue of having some idea of your
access patterns and having some control over how memory is used
(ie. often it makes sense to use dio and control the buffering
yourself).
Do you have any links to using/writing apps for dio?
Many Thanks
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