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Re: xfs_fsr question for improvement

To: xfs@xxxxxxxxxxx
Subject: Re: xfs_fsr question for improvement
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Fri, 16 Apr 2010 05:43:49 -0500
In-reply-to: <201004161043.11243@xxxxxx>
References: <201004161043.11243@xxxxxx>
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv: Gecko/20100317 Thunderbird/3.0.4
Michael Monnerie put forth on 4/16/2010 3:43 AM:

> To prevent this, xfs_fsr should do a "compress" phase after 
> defragmentation finished, in order to move all the files behind each 
> other:
> file 1GB
> file 1GB
> file 1GB
> file 1GB
> freespace 3600M
> That would also help fill the filesystem from front to end, reducing 
> disk head moves.

What happens if those are frequently written/appended files, such as logs or
mbox mail files, database files, etc?  If you pack them nose to tail with
this "compress" phase they will instantly be fragmented upon the next append
operation.  Leaving some free sectors at the tail end of a file is what
helps prevent fragmentation.  I don't think this compression would be a good
default behavior.  I think "packing" is probably a better term as
"compression" has a long standing connotation.

Sounds like you have a corner case.  If this "packing" was implemented,
maybe it would be best to make it a command line option only.


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