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Re: reading journal statistics



On Sep 17, 2003  10:37 -0500, Philip Molter wrote:
> Is there a way to get usage statistics on the journal device?  We
> are testing battery-backed NVRAM cards with extremely busy 1.7TB
> filesystems (mode data=journal) and we need to figure out what size
> NVRAM card we need.  I assume the journal size depends on how much
> writing you are doing and we can do simple theoretical calculations
> (writing 2.5MB/s, 60 seconds of journal would be max 150MB), but
> those numbers are probably off, maybe even completely wrong given
> the assumption.
> 
> Is there a way to check to exactly how much of the journal is
> waiting to be flushed to disk at any given time?  Is there a way
> to get I/O statistics of data in and out of the journal?
> 
> Honestly, I can't really find any information on how to get *any*
> stats on the journal device.

There isn't any, unfortunately.  However, it would be great to have.
You could probably work out things like average transaction size,
number of times journal was completely full, average fullness of
journal, etc pretty easily and export it via /proc.  Do this once
per transaction and you have some useful data.

Cheers, Andreas
--
Andreas Dilger
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/




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