2008-07-10 17:27:42

by Ric Wheeler

[permalink] [raw]
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:


The 4 threads chose the target subdirectory based on the time stamp,
rotating into a new subdirectory every 3 minutes or so.