[Linux-cluster] GFS journals

[Riaan van Niekerk]

Steve Maddison wrote:
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> Hi all,
> 
> We're looking at setting up a cluster and using GFS to share data
> between the individual nodes. Although our initial configuration would
> probably consist of about 3 nodes, it's important that we can easily add
> extra nodes in the future.
> 
> 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.

> 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.

Riaan

> Many thanks in advance for your responses.
> 
> 
> Kind regards,
> 
> - --
> Steve Maddison
> System Administrator
> Green Valley B.V.
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