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Re: file streams allocator behavior

To: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Subject: Re: file streams allocator behavior
From: Brian Foster <bfoster@xxxxxxxxxx>
Date: Sun, 26 Oct 2014 10:26:01 -0400
Cc: Richard Scobie <r.scobie@xxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <544C159E.8010408@xxxxxxxxxxxxxxxxx>
References: <544BF26F.6000708@xxxxxxxxxxxx> <544C159E.8010408@xxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.23 (2014-03-12)
On Sat, Oct 25, 2014 at 04:26:54PM -0500, Stan Hoeppner wrote:
> On 10/25/2014 01:56 PM, Richard Scobie wrote:
> > Stan Hoeppner said:
> > 
> >> How can I disable or change the filestreams behavior so all files go
> >> into the one AG for the single directory test?
> > 
> > Hi Stan,
> > 
> > Instead of mounting with -o filestreams, would using the chattr flag
> > instead help?
> > 
> > See
> > http://xfs.org/docs/xfsdocs-xml-dev/XFS_User_Guide/tmp/en-US/html/ch06s16.html
> 
> That won't help.  That turns it on (if it's not enabled by default these
> days).  I need to turn off the behavior I'm seeing, whether it's due to
> the filestreams allocator or default inode64.  Then again it may not be
> possible to turn it off...
> 
> Anyone have other ideas on how to accomplish my goal?  Parallel writes
> to a single AG on the outer platter edge vs the same to all AGs across
> the entire platter?  I'm simply trying to demonstrate the differences in
> aggregate bandwidth due to the extra seek latency of all AGs case.
> 

What about just preallocating the files? Obviously this removes block
allocation contention from your experiment, but it's not clear if that's
relevant to your test. If I create a smaller, but analogous fs to yours,
I seem to get this behavior from just doing an fallocate of each file in
advance.

E.g., Create directory 0, fallocate 44 files all of which end up in AG
0. Create directory 1, fallocate 44 files which end up in AG 1, etc.
>From there you can do direct I/O overwrites to 44 files across each AG
or 44 files in any single AG.

Brian

> Thanks,
> Stan
> 
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