journal on an ssd

Tobias Oetiker tobi at
Wed Sep 10 22:58:28 UTC 2008

Hi Chris,

Yesterday Chris Worley wrote:

> Note that I do have one to experiment with.
> What's a good way to measure journal performance, and/or in what cases do
> you need a faster journal (i.e. an EXT3 atop an MD device with big block
> stripes)?
> Chris

Well, the 'problem' we had to solve was the following:


- large HW raid6 array
- lvm on top
- many ext3 partitions

when there was a lot of write or meta data update activity on one
partition, performance on all other partitions went to 0.
(processes hanging for 10-20 seconds as soon as they accessed the
filesystem). I am sure that there is a bad-bad bug in the linux
kernel somewhere which is causing this, but all the upgrading and
patching did not help, the condition remained.

Until we moved the journals off to that external ssd.

Now I can copy partition A over to partition B and the server
remains nicely responsive. I am atributing that to the external

Obviously I would like to know how bad we are going to be had when
the ssd dies.


Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland tobi at ++41 62 775 9902 / sb: -9900

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