[Linux-cluster] Can I control journal size and placement in GFS? (need update for GFS 6.1?)

[Robert Peterson]

Filipe Miranda wrote:
> Hello,
> 
> I would like to know if the information below applies to the GFS 6.1?
> I guess that resource groups are the building blocks of the pool file 
> system
> management, but I the GFS 6.1 uses a tottaly different file system
> management (LVM2).
> (please correct me if I am wrong)
> 
> 
>   1. Can I control journal size and placement in GFS?
> 
>   Not really. The gfs_mkfs command decides exactly where everything
>   should go and you have no choice in the matter. The volume is carved into
>   logical "sections." The first and last sections are for multiple resource
>   groups, based roughly on the rg size specified on the gfs_mkfs 
> commandline.
>   The journals are always placed between the first and last section.
>   Specifying a different number of journals will force gfs_mkfs to carve 
> the
>   section size smaller, thus changing where your journals will end up.
> 
> 
> Thank you,
> Filipe Miranda

Hi Filipe,

I think you are confusing several different concepts here.

1. As far as I know, the term "pools" pertains to the older RHEL3 cluster code,
   and GFS 6.1 doesn't know about pools.
2. The RGs (Resource Groups) are building blocks of the GFS file system.
3. The LVM2 layer is completely separate from GFS.  In other words, you can 
   make a GFS file system inside (I think of it as inside anyway) a Logical
   volume of LVM2.  You can also make a GFS file system on a file system
   partition without LVM2.
4. Yes, the FAQ entry you referenced does apply to GFS 6.1 and all other
   releases of GFS as far as I know.  It does not, however, address GFS2 directly.
   GFS2 has a slightly different format.  Even so, you can't really control 
   the placement of a journal in GFS2 either.

Regards,

Bob Peterson
Red Hat Cluster Suite