linux-ext4 - Does Ext4 support parallel write similar to XFS?

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Date:	Wed, 25 Jan 2012 10:49:59 +0530
From:	Amit Sahrawat <amit.sahrawat83@...il.com>
To:	xfs@....sgi.com, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Dave Chinner <david@...morbit.com>
Subject: Does Ext4 support parallel write similar to XFS?

In XFS we can write parallel (i.,e we can make use of allocation
groups for writing process). If the files are kept in individual
directories, there is a possibility that first the blocks for that
files be used from individual allocation groups. If I start ‘4’
writing process(cp 100MB_file /<dirnum>/) – after writing is finished
– if I check the bmap – it does shows that initial allocation was from
individual allocation groups.
Even though in Ext4 also we do have groups – but I am not able to get
behavior similar to XFS.
If I check the file extents – the extents are in mixed form, the
allocation pattern is also very fragmented.

Please share more on this. Also, if there is a possible exact test
case to check for parallel writes support.

Thanks & Regards,
Amit Sahrawat
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