[Linux-cluster] which journaling file system is used in GFS?

[Wendy Cheng]

Ja S wrote:
> Hi, All:
>
> >From some online articles, in ext3, there are journal,
> ordered, and writeback three types of journaling file
> systems. Also in ext3, we can attach  the journaling
> file system  to the journal block device located on a
> different partition. 
>   

GFS *is* a journaling filesystem, same as EXT3. All journaling 
filesystem has journal(s) which is (are) almost an equivalence of 
database logging. The internal logic of journaling could be different 
and we call it journaling "mode".
> I have not yet found related information for GFS.
>
> My questions are:
>
> 1. Does GFS also support the three types of journaling
> file systems? If not, what journaling file system is
> used in GFS?
>   
So please don't use "journaling file system" to describe journal. 
Practically, GFS has only one type of journaling (write-back) but it 
supports data journaling thru "gfs_tool setflag" command (see "man 
gfs_tool). GFS2 has improved this by moving the "setflag" command into 
mount command (so it is less confusing) and has been designed to use 
three journaling modes (write-back, order-write, and data journaling, 
with order-write as its default). It (GFS2), however, doesn't allow 
external journaling devices yet.

I understand moving ext3 journal into an external device and/or moving 
journaling mode from its default (order write) into "write back" can 
significantly lift its performance. These tricks can *not* be applied to 
GFS.

-- Wendy