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Re: Is persistant preallocation possible?

To: Jeff Zheng <Jeff.Zheng@xxxxxxxxxx>
Subject: Re: Is persistant preallocation possible?
From: Nathan Scott <nathans@xxxxxxxxxx>
Date: Tue, 25 May 2010 12:26:14 +1000 (EST)
Cc: xfs@xxxxxxxxxxx
In-reply-to: <9256268935CF66428AC10E736C91455F024036@xxxxxxxxxxxxxxxxxxxxxxxx>
----- "Jeff Zheng" <Jeff.Zheng@xxxxxxxxxx> wrote:

> Hi,
> 
> We are trying to control where the files are being allocated on the
> disks, and we tried xfs preallocation. What we found is that each time
> the file being reopened the location of the pre-allocated space could
> change (not all the time). Is there a way to do persistent
> preallocation in xfs, like the same file will always be on the same
> location on the disk given that the requested size doesn’t change?
> 

Sounds like you are truncating the file (on open?), and hence discarding
the preallocation.  XFS preallocation is persistent already, so I think
something you are doing must be discarding those preallocated extents.

Could you post a test program, or sequence of xfs_io commands, that would
demonstrate the problem?

cheers.

-- 
Nathan

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