Phil Stracchino wrote:
> On 04/08/10 03:53, Craig Ringer wrote:
>> BTW, When I suggested that greater write concurrency would be desirable
>> and should be easier, Phil Stracchino raised some concerns about
>> concurrent writes to a file system increasing fragmentation and hurting
>> overall performance. Rather than just wave my hands about that I've put
>> together a testing tool for concurrently writing big files from multiple
>> threads that optionally uses posix_fallocate to pre-allocate ahead in
>> chunks up to total file size. It tracks per-thread and total runtime and
>> time spent in write() and posix_fallocate() calls. I'm doing some tests
>> with it now and will post it to the bacula-devel list too. I'm planning
>> on testing the real effects of various levels of concurrent writes on
>> common file systems with it using a controlling shell script and will
>> report back when that eventually finishes.
> 
> I'll be interested to see those results.  Which filesystems are you testing?

I'm interested in ext3, ext4 and xfs. I should probably look at zfs too,
but don't have any hosts that it runs on usefully and don't really have
any personal interest in it.

I've posted the tool's sources & makefile to the devel list along with
some preliminary notes. So far it looks like posix_fallocate is, as
expected, a win if you know the volume size (or a reasonable
approximation of it) in advance, and not much help or a loss if you
don't so you posix_fallocate(...) smaller chunks progressively. Further
info will appear on -devel once I've put it together.

--
Craig Ringer

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