Hi Zheng,

* On Fri, Jan 13, 2012 at 04:41:16PM -0500, Zheng Da [off-list ref] wrote:

Hello,

I'm looking for a FS in Linux that supports concurrent direct IO write.
ext4 supports concurrent direct IO read if we mount it with dioread_nolock,
but doesn't support concurrent writes. XFS doesn't support concurrent
direct IO at all. It locks the inode exclusive if it's direct IO. I tried
btrfs, and it seems it doesn't support concurrent direct IO either though I
haven't looked into its code.
Is there a local FS that support concurrent direct IO write? It seems NFS
supports it (
http://kevinclosson.wordpress.com/2011/08/12/file-systems-for-a-database-choose-one-that-couples-direct-io-and-concurrent-io-whats-this-have-to-do-with-nfs-harken-back-5-2-years-to-find-out/),
but I'm looking for local FS.

Thanks,
Da

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XFS locks inode exclusive only if it is an unaligned Direct 
IO, which is apparently done to prevent race conditions -- 
refer to this  http://oss.sgi.com/archives/xfs/2011-01/msg00157.html 
Also the behavior of Ext4 under dioread_nolock is supported 
by XFS by default and in a much better way. Also Ext4 is the only 
one which uses DIO_LOCKING while doing direct io.



Regards,
-- 
Raghavendra Prabhu
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www: wnohang.net
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