Re: file streams allocator behavior

From: Stan Hoeppner <stan@hardwarefreak.com>
To: Brian Foster <bfoster@redhat.com>
Cc: Richard Scobie <r.scobie@clear.net.nz>, xfs@oss.sgi.com
Subject: Re: file streams allocator behavior
Date: Sun, 26 Oct 2014 12:26:57 -0500	[thread overview]
Message-ID: <544D2EE1.3080304@hardwarefreak.com> (raw)
In-Reply-To: <20141026142559.GA61711@bfoster.bfoster>

On 10/26/2014 09:26 AM, Brian Foster wrote:
> 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.

I figured preallocating would get me what I want but I've never used
fallocate, nor dd into fallocated files.  Is there anything special
required here with dd, or can I simply specify the filename to dd, and
make sure bs + count doesn't go beyond EOF?

Thanks,
Stan

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