Hi there, I have been experiencing some slowness with an ext4 filesystem. I will try to explain and hopefully somebody can identify whether this is "normal" or not. Sorry if I am in any sense unscientific - filesystems are somewhere near the edge of my computer science knowledge :) Basically I am involved with doing some development on the Ruby on Rails web app framework, and the automated tests for one component (Active Record) does a lot of reading/writing from a database. I realised that the test suite was running significantly slower for me than for another developer, so I started to investigate. First I created an unencrypted partition and put my databases on it, as I had previously had everything encrypted. This made it somewhat faster, but not massively. I then used iotop to see what was going on when I ran the tests. I discovered that the process jbd2/sda3-8 was doing *lots* of IO when I run these tests. I did some googling and tried a few things. Removing the journal solved the problem (as would be expected, I guess), but also recreating the partition as ext3 rather than ext4 solved it too (which perhaps indicates a regression?) When I say 'solved', I mean it took a single run of this particular test suite from say 4.5 minutes to more like 60-80 seconds. I found some other people reporting a similar problem: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/607560 They complain of the jbd2 process running every few seconds. This is something I had not noticed before, but I can observe this on my system too. It runs and uses a lot of IO for a short period of time maybe every 2 seconds. So I think I am experiencing the same problem. FWIW, using the noatime option does not help at all. Also, I have tried using a very recent kernel build with no success. And I have run iotop on another laptop (which also has an ext4 partition) and I cannot observe this frequent running of jbd2. So: does this sound like a bug, and if so, what can be done? I'm very happy to provide any additional information as needed. Many thanks, Jon
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