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Old 04-13-2005, 01:22 PM   #1
lucky123
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journaling modes in ext3 file system


I am a linux newbie and a great fan of linux.This is my first
query to your forum.Please clear me in the simplest language
for the following queries.

Q. Ext3 file system has the features of journaling that contains

filesystem's metadata.What are those metadata and where the journal is
located in my system.
Also it provides much higher data integrity.What does that mean.
Also tell me about the 3 journaling modes.
ordered , writeback and journaled.

Which command should i use to know about the three modes?

Also can we can use reiserfs file system in Fedora distribution.

Please somebody help me out in the simplest language.
 
Old 04-14-2005, 10:18 PM   #2
Thoreau
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Hans Reiser is a pretty smart fella, and he invented reiserfs. His website with all the info you need is http://www.namesys.com/. I'm telling you about this first, because reiserfs came before ext3. Years before, in fact. Here is the correllary data for reiserfs:

data=ordered / journal / writeback

Specifies the journalling mode for file data. Metadata is always journaled.

journal

All data is committed into the journal prior to being written into the main file system.

ordered

This is the default mode. All data is forced directly out to the main file system prior to its metadata being committed to the journal.

writeback

Data ordering is not preserved - data may be written into the main file system after its metadata has been committed to the journal. This is rumoured to be the highest-throughput option. It guarantees internal file system integrity, however it can allow old data to appear in files after a crash and journal recovery.

Example:
mount -t reiserfs -o data=writeback /dev/sdb1 /mnt/scsi-disk-b

Theodore T'so and Stephen Tweedie helped to invent ext3. Mostly due to pressure from reiserfs at the time. ext2 seemed ghetto in comparison, so he bucked up and released ext3 with backwards compatibility to ext2. He is here:
http://www.kernelthread.com/hotshots/pages/tytso0.html

The mount options for ext3 are:

"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.


And does Fedora support Reiserfs. I know that all linux kernel have Reiserfs support, but whether Fedora has it as an option defaulted on install, I'm not sure.

Redhat stopped including it as an option at various times over the years and defaulted to ext3- since their people invented it. At one point reiserfs was not available. And at one point later, it was. So, I don't know. You'll have to ask a Fedora Core 3 user if reiserfs is compiled in as a module in the default installation.

Hope this short intro answered your question. Take care.

Last edited by Thoreau; 04-14-2005 at 10:19 PM.
 
Old 04-14-2005, 11:03 PM   #3
masonm
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Actually kernels only have reiserfs support IF it's been compiled into the kernel. Otherwise, if it's compiled as a module, an initrd is required to boot a reiserfs partition. If reiserfs is not an available option for you at install, don't worry about it, use the ext3 option.

The only way to know for sure if reiserfs support is compiled in is to do the install and see if it's an option when you format the partitions.

Thoreau gave a very concise explaination of the different journaling modes. If you want to learn more, google is your friend.
 
  


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