Hi all!
Since the system default is running ext3 the journal file system in FC2 and now are still using in FC3. Is it a safety file system ?
Becuase I saw the books didn't stated the different and what would it happen if the system crash in ext2 or ext3 ?
Ringo
Wong Kwok-hon wrote:
Since the system default is running ext3 the journal file system in FC2 and now are still using in FC3. Is it a safety file system ?
Becuase I saw the books didn't stated the different and what would it happen if the system crash in ext2 or ext3 ?
Ringo
Ext3 has journaling. What this means for you is that the system journals disc activity so as if somethin' horrible happens; let's say a power failure in the middle of a disc write or something like that, then the journal will ease recovery. The journal allows the system to replay the last actions taken up to the point of failure and then continue on as if nothing ever happened. Ext3 is the default for Fedora.
Ext2 is the exact same file system basically, other than it lacks journaling. What this means for you is if the machine dies in the middle of a disc write; as mentioned above, the machine will have to fsck the disc. This can be a very long and arduous process in comparison to the replay of a journal in ext3. On the other hand, ext2 is much faster than ext3 simply because it lacks the journaling system. If you want to know which one to choose, use ext3.
If you're worried about speed, I don't think it's going to be something you notice too too much. Ext3 can be tweaked to provide better speed, if mounted with certain options. What those are, is best found by googling or searching the archives. I've seen those mentioned here before.
A good source to find this information out is by using google too. If you want a real break down of it, google can provide you with an indepth discussion on the matter from developers and benchmarks.
HTH
Alex White
On Thu, 2004-12-02 at 18:31 -0600, Alex White wrote:
Ext3 has journaling. What this means for you is that the system journals disc activity so as if somethin' horrible happens; let's say a power failure in the middle of a disc write or something like that, then the journal will ease recovery. The journal allows the system to replay the last actions taken up to the point of failure and then continue on as if nothing ever happened. Ext3 is the default for Fedora.
Actually, there's more to it than that. There are three different journaling modes supported by ext3 as quoted from the Linux source tree in Documentation/filesystems/ext3.txt and please note the default is metadata only journaling.
Data Mode --------- There's 3 different data modes:
* writeback mode In data=writeback mode, ext3 does not journal data at all. This mode provides a similar level of journaling as XFS, JFS, and ReiserFS in its default mode - metadata journaling. A crash+recovery can cause incorrect data to appear in files which were written shortly before the crash. This mode will typically provide the best ext3 performance.
* ordered mode In data=ordered mode, ext3 only officially journals metadata, but it logically groups metadata and data blocks into a single unit called a transaction. When it's time to write the new metadata out to disk, the associated data blocks are written first. In general, this mode perform slightly slower than writeback but significantly faster than journal mode.
* journal mode data=journal mode provides full data and metadata journaling. All new data is written to the journal first, and then to its final location. In the event of a crash, the journal can be replayed, bringing both data and metadata into a consistent state. This mode is the slowest except when data needs to be read from and written to disk at the same time where it outperform all others mode.
Wong Kwok-hon wrote:
Becuase I saw the books didn't stated the different and what would it happen if the system crash in ext2 or ext3 ?
A journalling filesystem (as I understand it) keeps track of changed inodes in a journal before making the actual change to the filesystem. Thus, if a system crash occurs during the actual change in question, the journal can be rewound and the transactions undone, thus keeping the filesystem in a consistent state (you still lose the data from that incomplete transaction). ext2, on the other hand, does no such thing, and if the system crashes with the filesystem in an inconsistent state, you will need to spend a lot more time figuring out what's wrong with it, and there are more potential things to go wrong with it (the dreaded lost+found).
Brian
On Fri, Dec 03, 2004 at 08:17:39AM +0800, Wong Kwok-hon wrote:
Since the system default is running ext3 the journal file system in FC2 and now are still using in FC3. Is it a safety file system ?
Becuase I saw the books didn't stated the different and what would it happen if the system crash in ext2 or ext3 ?
http://www.redhat.com/docs/manuals/enterprise/RHEL-3-Manual/admin-guide/s1-s...
On Thu, 2004-12-02 at 18:17, Wong Kwok-hon wrote:
Hi all!
Since the system default is running ext3 the journal file system in FC2 and now are still using in FC3. Is it a safety file system ?
Becuase I saw the books didn't stated the different and what would it happen if the system crash in ext2 or ext3 ?
I remember reading the release notes, I believe from FC2; it mentioned that if the system lost power, there was only a *tiny* chance something could be written wrong to the filesystem, whereas if the thing were warm, and merely reset, no chance.
Does this help?
ext3 is also [a little more] compatible with the new LVM (which you're gonna love). As to the safety of the choices? I'd say they both are quite safe. Lord knows I've had enough power brownouts here to give it the chance!