[nylug-talk] extfs journalling percentage

[Chris Knadle]

On Tuesday 27 May 2008, Michael Bubb wrote:
> Taking home as an example the actual numbers are:
> /dev/sda6             72437948  49776256  18982008  73% /home
>
> The file system in this case is ext3.
> On this and other similar servers in my company, I have noticed a 5.1%
> 'overhead' on the difference between the partition's capacity and its
> amount usable.
> I realize this is the journal and the blocks reserved for root.
>
> Looking at the man page for mkfs.ext3 I see that there is a '-m' flag
> which can adjust this. Do you have recommendations for this? I do not
> know much about filesystems and tend to leave the default settings
> alone...
>
> If I understand correctly the actual journal is not that big. Most of
> this 5% is reserved so that a superuser has access to  an otherwise
> full partition. Do you need 5% for this? (ie if you have a 250G
> parttion do you need 13G reserved).
>
> Thanks as always
>
> Michael

   I'm not 100% positive, but I don't think the ext3 journal counts in that 5% 
reserved for root-only usage.  Mainly I think that this is space set aside 
for root for having a place to do emergency filesystem repair, like using 
debugfs or similar utilities.  I've often wondered the same thing you have 
and on occasion I've set up a test box with 0% reserved space and nothing 
terrible happened, but then again I also didn't have a problem such that I'd 
need a space to work with debugfs, etc.
   i.e. I believe whether you need it or not is a question of your own 
administration needs rather than the filesystem's own requirements.

   -- Chris

-- 

Chris Knadle
Chris.Knadle at coredump.us