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Date: Tue, 6 Jul 2010 18:01:01 -0400 From: tytso@....edu To: Eric Sandeen <sandeen@...hat.com> Cc: Daniel Taylor <Daniel.Taylor@....com>, linux-ext4@...r.kernel.org Subject: Re: inconsistent file placement On Tue, Jul 06, 2010 at 01:59:34PM -0500, Eric Sandeen wrote: > However, from the test description it looks like it is writing > a file to the root dir, so there should be no parent-dir random spreading, > right? Hmm, yes, I missed that part of Daniel's e-mail. He's just writing a single file. In that case, Amir is right, the only thing which would be causing this is the colour offset, at least for ext2 and ext3. This is avoid fragmented files caused by two or more processes running on different CPU's all writing into the same block group. In the case of ext4, we don't use a pid-determined colour algorithm if delayed allocation is used, and the randomness is caused by the writeback system deciding to write out different chunks of pages first. The way to fix this when writing large files is to use fallocate(2) when writing a large file, so it can be allocated contiguously. In any case, Daniel, if you want the best results for your benchmark, use ext4, and tweak the script slightly: touch /DataVolume/hex.txt fallocate -l 5G /DataVolume/hex.txt for i in 0 1 2 3 4 do dd if=/hex.txt of=/DataVolume/hex.txt bs=64k conv=notrunc \ oflag=direct,append done Best regards, - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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