[Linux-cluster] GFS journals

[Steve Maddison]

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Riaan van Niekerk wrote:
> 
> Steve Maddison wrote:
> 
> I've read that each node requires its own journal on the GFS filesystem
> and that it's impossible to add journals without expanding the
> filesystem. 
> 
>> small correction - to be able to add journals, you need unused space on
>> the underlying LV or partition.
> 

Ok - that's different to what I've read, although In our case it doesn't
really matter. Suffice to say that we don't want to be adding
significant amounts of storage solely to support an increase in the
number of nodes (and therefore journals).

> My query is therefore whether it's in any way detrimental to
> specify a large number of journals (I'm thinking along the lines of 16
> or 32 in our case) when creating the filesystem if these are unlikely to
> ever be used? I realise each journal will incur a cost in terms of
> storage space, but I'm willing to make the trade-off for the sake
> scalability.
> 
>> We created our GFS with 32 journals (during testing and in production)
>> despite having only 6 nodes mounting it currently. We have not noticed
>> any overhead w.r.t. mounting the GFS. I don't know what the journal size
>> is, but we are not talking GB's per journal, AFAIK.
> 

The default is apparently 128Mb per journal, although you can specify a
different size during creation. So we're looking at a few GB _total_ for
all journals, which I'm pretty sure I can afford ;-)

Thanks for sharing your experience on this matter.

- --
Steve Maddison
System Administrator
Green Valley BV
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