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Date: Tue, 06 Jul 2010 13:59:34 -0500 From: Eric Sandeen <sandeen@...hat.com> To: tytso@....edu CC: Daniel Taylor <Daniel.Taylor@....com>, linux-ext4@...r.kernel.org Subject: Re: inconsistent file placement tytso@....edu wrote: > On Mon, Jul 05, 2010 at 06:49:34PM -0700, Daniel Taylor wrote: >> I realize that it is enerally not a good idea to tune >> an operating system, or subsystem, for benchmarking, but >> there's something that I don't understand about ext[234] >> that is badly affecting our product. File placement on >> newly-created file systems is inconsistent. I can't, >> yet, call it a bug, but I really need to understand what >> is happening, and I cannot find, in the source code, the >> source of the randomization (related to "goal"???). > > In ext3, it really is random. The randomness you're looking for can > be found in fs/ext3/ialloc.c:find_group_orlov(), when it calls > get_random_bytes(). This is responsible for "spreading" directories > so they are spread across the block groups, to try to prevent > fragmented files. Yes, if all you care about is benchmarks which only > use 10% of the entire file system, and for which the benchmarks don't > adequately simulate file system aging, the algorithms in ext3 will > cause a lot of variability. 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? -Eric -- 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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