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allocsize mount option

To: "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
Subject: allocsize mount option
From: Peter Vajgel <pv@xxxxxx>
Date: Thu, 20 Jan 2011 20:41:19 +0000
Accept-language: en-US
Thread-index: Acu44SnRhSXb3vU+Ra2sCPFBekjffg==
Thread-topic: allocsize mount option
We write about 100 100GB files into a single 10TB volume with xfs. We are using 
allocsize=1g to limit the fragmentation with a great success. We also need to 
reserve some space (~200GB) on each filesystem for processing the files and 
writing new versions of the files. Once we have only 200GB available we stop 
writing to the files. However with allocsize it's not that easy - we see +/- 
100GB added or taken depending if there are still writes going and if the file 
was reopened ... Is there a way to programmatically disable allocsize 
speculative preallocation once we exceed certain threshold and also return the 
current speculative preallocation back to the free space (without closing the 
file)?

Thx

Peter Vajgel

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