> From: Narender Rao <[EMAIL PROTECTED]> > Subject: Re: [twincling] ext3 filesystem mount query > Sent: 28 Dec '06 12:24 > > Hi Saifi, > > This is what i found over net: > > > The EXT3-fs message is just telling you it mounted the fs OK. It's > also telling you what form of journaling you are using. > > ext3 has 2 formats of journal: > version 1 - default and only possibility for ext3 releases 0.0.3* > and earlier > version 2 - default for filesystems created with 0.0.4 and later > > Version 2 journals support additional semantics required to allow > metadata journaling, and provide 2 new forms of journaling - ordered > and writeback. Both V1 & V2 journals support data journaling (where > everything that would go to disk is journaled). > > The CHANGES file in the distribution says this: New mount options: > > "mount -o journal=update" > > Mounts a filesystem with a Version 1 journal, upgrading the > > journal dynamically to Version 2. > > "mount -o data=journal" > > Journals all data and metadata, so data is written twice. This > > is the mode which all prior versions of ext3 used. > > "mount -o data=ordered" > > Only journals metadata changes, but data updates are flushed to > > disk before any transactions commit. Data writes are not atomic > > but this mode still guarantees that after a crash, files will > > never contain stale data blocks from old files. > > "mount -o data=writeback" > > Only journals metadata changes, and data updates are entirely > > left to the normal "sync" process. After a crash, files will > > may contain stale data blocks from old files: this mode is > > exactly equivalent to running ext2 with a very fast fsck on reboot. > > > > Ordered and Writeback data modes require a Version 2 journal: if you do > > not update the journal format then only the Journaled data will be > > allowed. > > The default data mode is Journaled for a V1 journal, and Ordered for V2. >
Hi Narender: That was a great overview of ext3fs as I had no idea about how ext3fs works. I am still keen to know, what is the difference between "ordered" and "writeback" ? May be Namita can help us out here. thanks Saifi.
