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
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