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Preallocation with direct IO?

To: "hch@xxxxxxxxxxxxx" <hch@xxxxxxxxxxxxx>, "david@xxxxxxxxxxxxx" <david@xxxxxxxxxxxxx>, "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
Subject: Preallocation with direct IO?
From: "amit.sahrawat83@xxxxxxxxx" <amit.sahrawat83@xxxxxxxxx>
Date: Thu, 29 Dec 2011 13:10:49 +0000
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Reply-to: amit.sahrawat83@xxxxxxxxx
I am using a test setup which is doing write using multiple threads using 
direct IO. The buffer size which is used to write is 512KB.
After continously running this for long duration - i observe that number of 
extents in each file is getting huge(2K..4K..). I observed that each extent is 
of 512KB(aligned to write buffer size). I wish to have low number of 
extents(i.e, reduce fragmentation)... In case of buffered IO- preallocation 
works good alongwith the mount option 'allocsize'. Is there anything which can 
be done for Direct IO?
Please advice for reducing fragmentation with direct IO.
Thanks & Regards,
Amit Sahrawat
Sent from my Nokia phone

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