From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ric Wheeler Subject: Re: suspiciously good fsck times? Date: Thu, 10 Jul 2008 13:27:40 -0400 Message-ID: <4876468C.2040005@redhat.com> References: <4876025A.80909@gmail.com> <20080710151822.GA25939@mit.edu> <48762F9F.5070308@redhat.com> <48763564.2090505@redhat.com> <20080710172117.GE10402@mit.edu> Reply-To: rwheeler@redhat.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Eric Sandeen , linux-ext4@vger.kernel.org To: Theodore Tso Return-path: Received: from mx1.redhat.com ([66.187.233.31]:53834 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757464AbYGJR1m (ORCPT ); Thu, 10 Jul 2008 13:27:42 -0400 In-Reply-To: <20080710172117.GE10402@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: 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