Preallocation with direct IO?

[amit.sahrawat83 at gmail.com]

Hi,
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
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