[Linux-cluster] Gfs_data vs gfs_journal

[Erling Nygaard]

Ben

You can indeed have external journals with GFS.

As Mike was saying, you can specify a subpool with type "gfs_journal".
And since you easily can specify what device the subpool is on you decide 
where the journal is.

This feature has been in GFS since 'a looong time ago' and unless there 
have been changes to this in OpenGFS this feature works in the same way in 
all versions of GFS :)

As Mike pointed out, this was originally done in case of Solid State 
Disks, where having the journals on the SSD could prove speedup. Due to 
lack of SSDs this has never really been tested much...


Erling



On Wed, Jul 07, 2004 at 08:16:59AM -0700, Cahill, Ben M wrote:
> Oops, based on Michael's response, I realized that mine might be not
> quite right.  Both data and journal *space* are necessary, but the
> journals can be created, by default, within the filesystem device, with
> no need for gfs_journal entry in config file.
> 
> BTW, OpenGFS has supported external journals for over a year at this
> point ... would this be a useful feature for GFS?
> 
> -- Ben --
> 
> Opinions are mine, not Intel's
> 
> > -----Original Message-----
> > From: linux-cluster-bounces at redhat.com 
> > [mailto:linux-cluster-bounces at redhat.com] On Behalf Of Cahill, Ben M
> > Sent: Wednesday, July 07, 2004 11:07 AM
> > To: linux-cluster at redhat.com
> > Subject: RE: [Linux-cluster] Gfs_data vs gfs_journal
> > 
> > They are both necessary.
> > 
> > gfs_data is the device/partition for filesystem data (i.e. files and
> > on-disk metadata).
> > 
> > Each node in the cluster also needs a separate journal 
> > device/partition
> > in which to redundantly record metadata, to enable the filesystem to
> > recover gracefully from node failure/crash.
> > 
> > There's some documentation about this in the OpenGFS project:
> > 
> > opengfs.sourceforge.net/docs.php
> > 
> > CAUTION:  OpenGFS is *not* the same as current RedHat GFS; many things
> > (e.g. lock protocols) are different ... but the basic idea is 
> > the same.
> > See WHATIS-OpenGFS, and HOWTO-generic, just to see if they help you
> > understand.  But remember to rely on current RedHat GFS docs 
> > for current
> > installation, components, and capabilities info.
> > 
> > -- Ben --
> > 
> > Opinions are mine, not Intel's
> > 
> > > -----Original Message-----
> > > From: linux-cluster-bounces at redhat.com 
> > > [mailto:linux-cluster-bounces at redhat.com] On Behalf Of 
> > Richard Mayhew
> > > Sent: Wednesday, July 07, 2004 6:24 AM
> > > To: Discussion of clustering software components including GFS
> > > Subject: [Linux-cluster] Gfs_data vs gfs_journal
> > > 
> > > Hi,
> > > 
> > > Could some one explain or point me in the right direction in the
> > > differences between gfs_data and gfs_journal in the pool 
> > config file.
> > > 
> > > Which is the better option, and why?
> > > 
> > > Thanks
> > > Richard.
> > > 
> > > --
> > > Linux-cluster mailing list
> > > Linux-cluster at redhat.com
> > > http://www.redhat.com/mailman/listinfo/linux-cluster
> > > 
> > > 
> > 
> > --
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> > 
> > 
> 
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-- 
Erling Nygaard
nygaard at redhat.com

Red Hat Inc