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Date: Thu, 10 Jul 2008 13:27:40 -0400 From: Ric Wheeler <rwheeler@...hat.com> To: Theodore Tso <tytso@....edu> CC: Eric Sandeen <sandeen@...hat.com>, linux-ext4@...r.kernel.org Subject: Re: suspiciously good fsck times? Theodore Tso wrote: > On Thu, Jul 10, 2008 at 11:14:28AM -0500, Eric Sandeen wrote: > >> Val & I talked about this a little, and came to the conclusion that >> directory fragmentation might be a pretty big part of it. >> > > Hmm, could be. Let's see. Ric said 46.5 million files, I don't know > how big the filenames were, but let's assume a directory entry size of > 32, so that means if we assume perfect packing, 128 directory entries > per 4k block. Let's use 100 directory entries/blok just to make the > math easyer, so that's 465,000 blocks. If we assume a 10ms seek time, > and that the blocks are totally scattered, that's 4650 seconds, or > 1.29 hours. So that's roughly within the ballpark that Ric measured. > > - Ted > (changing cc to the real list instead of ext4 owner - sorry!) The file names are 40 bytes long, (6 initial bytes of time stamp with 24 random bytes at end of name. For example: 451aeb61ead89~~~DYASX8LYL4NAUWK3WI187VRP The 4 threads chose the target subdirectory based on the time stamp, rotating into a new subdirectory every 3 minutes or so. ric -- 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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