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



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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