On Dienstag, 9. August 2011 Marc Lehmann wrote:

On Tue, Aug 09, 2011 at 12:10:48PM +0200, Michael Monnerie 

[off-list ref] wrote:

quoted

First of all, please calm down. Getting personal is not bringing us
anywhere.

Well, it's not me who's getting personal, so...?

A single rant from a dev shouldn't hurt one too much. He might have been 
sitting in front of some code during 72 hours, his eyes already being in 
16:9 format staring at a weird bug... It's OK to strike back once, but 
then be cool again and work at the problem.
 

As has been reported on this list, this option is really harmful on
current xfs - in my case, it lead to xfs causing ENOSPC even when the
disk was 40% empty (~188gb).

Was this the "NFS optimization" stuff? I don't like that either.
 

Well, if it were one fragment, you could read that in 4-5 seconds, at
374 fragments, it's probably around 6-7 seconds. Thats not harmful,
but if you extrapolate this to a few gigabytes and a lot of files,
it becomes quite the overhead.

True, if you have to read tons of log files all day. That's not my 
normal use case, so I didn't bother about that until now.

That allocsize option is no longer reasonable with newer kernels, as
the kernel will reserve 64m diskspace even for 1kb files
indefinitely.

Just "as long as the inode is cached" or something, I remember that 
"echo 3 >drop_caches" cleans that up. Still ugly, I'd say.
 

If you find a way of recreating files without appending to them, let
me know.

Seems we have a different meaning of "append". For me, append is when an 
existing file is re-opened, and data added just to the end of it.
 

quoted

And maybe he could use it for optimizations. Is there any tool on
Linux to record such I/O patterns?

I presume strace would do, but thats where the "lot of work" comes
in. If there is a ready-to-use tool, that would of course make it
easy.

It's a pity that such a generic tool doesn't existing. I can't believe 
that. Doesn't anybody have such a tool at hand?

-- 
mit freundlichen Grüssen,
Michael Monnerie, Ing. BSc

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