Slashdot Mirror
Ext3 Filesystem Explained
sheckard writes: "The next installment of the wonderful Advanced filesystem implementor's guide, part 7, details the ext3 filesystem in all of its glory. This is another great voyage into the world of journaling filesystems, and ext3 has been rock-solid in my experience."
On my new machine I installed linux as my primary os, expecting soon get tired of it (again) and reconfigure a dual boot system windows as my primary OS. While installing linux, I didn't think much(since I would soon be destroying the partition anyway) and installed the system on reiserfs. To my surprise that didn't happen and unreliability of reiserfs started to bother me more and more. And with this article I'm convinced that ext3 is what I want. Now, how do I convert from ReiserFS to ext3? I have plent of empty space on a soon to be destroyed ntfs partition and a cd writer, so backing up existing data is no problem, but simply copying back files will not do the trick, right?
Gentlemen, you can't fight in here, this is the War Room!
Although I did enjoy the paragraph on filesystem journaling -- After pulling my one of my [gasp] Win2000 servers offline the other night to do a defrag, I could appreciate the fact that a developer could tweak Ext3 to do some neat things. (ahh, for linux, at least) Like when I save and resave files on a test server, the journaling approach could be made more efficient by only saving the changed data! (not the whole freakin fragmented file)
Now the question could be -- Is there someone who will step up to the plate and produce several custom filesystems. The article points out that there is no "best" file system, but given the options, I'm sure the teckie endusers could tweak settings to meet their needs, be it server or desktop.
Newt-dog
My Doctor prescribed daily nasal saline irrigation, hehe
I've tried both, but when I played with XFS it took forever to rm -rf a 2 GB directory. Was it me, or is XFS extremely slow with removing lots of files? If so, is this because if takes forever to update the journal?
I hope that joe public will eventually realize journalling filesystems don't guarantee data integrity in the event of an unclean system shutdown.
I've converted over to ext3fs, and am curious about one thing: resizing the ext3fs partitions. I know Partition Magic can resize ext2fs partitions with no difficulty, and Linux won't miss a beat. If the file systems are cleanly unmounted, as during a shutdown, and the ext3fs partitions are resized using Partition Magic, will there be problems? Is there anything in the journal that would make the kernel panic and puke on the newly changed partitions? I have no plans to do this; I'm just curious what would happen if I did.
"Anyone that has ever gotten an idea based on any of my work and done something better with it-good for you."--J.Carmack
Do you still need the every 20th mount fsck???
- Pimp
I like computers, women and computers... in that order...
Yet another Red Hat revolutionary product that the rest of the distributions promptly ignore. And with good cause.
This talk of ext3 being faster than Reiser or XFS is crap. It's not faster, and on IDE hardware the journaling capabilities are offset by the way the IDE drives work. Ext3 is the weaker of the bunch on IDE hardware, to the point that you might as well not even use it. It seems the point of ext3 is to eliminate the need of fsck and not the benefits that can be had with journaling (as in XFS's xfsdump and xfsrestore).
If you want a good journaling filesystem, use Reiser or XFS on FAST drive hardware. If you're not up to making the investment in SCSI or ATA 100 drives and insist upon running XFS or Rieser on your 5200 rpm 10 gig IDE drive, of *course* it'll be slow.
ext2 doesn't have a 2GB file size limit. That was a operating system limit which went away somewhere in the middle 2.2.x stable series.
Further, ext3 is not the-next-version-of-EXT. It is an extention of ext2 which is fully compatible with ext2. Think of ext2 as two things: the format of bits on the disk, and the code to read/write those bits. Ext3 keeps the same format (actually with compatable extentions), but mostly it changes the code for reading/writing to the disk (journelling).
The ext2 filesystem is tried and true. You can go back and forth between ext2 and ext3 with no reformating or issueing of commands other than the mount command.
ReiserFS is a more "sophisticated" filesystem than ext[23], and XFS is a more "sophisticated" filesystem than ReiserFS. But I keep "sophisticated" in quotes because the utility, reliability, and speed of a FS relies more on your usage patterns, than on the genius of the filesystem designers/coders.
FFS-style: ext2,ufsFFS+journel: ext3, ufs+
B+tree directories, B+tree block layout, Journelling: ReiserFS
B+tree directories, B+tree block layout, extents, Journelling : XFS, JFS
Loggin FS: VxFS (my favorite)
I use ext3 at home. Good speed, no need to tar up all my files..reformat drives..untar all my data, journelling, mainline kernel support, tried and true.
One place I would seriously consider ReiserFS is for home directories. The place it really shines is constantly reading and writing lots of "small" files (small ~50k). For Gnome and KDE config files, Mozilla disk caches, CVS checkouts, and untaring of source, ReiserFS is going to be a leader of the benchmarking pack. You'll notice the difference.
But don't get into holy wars over FS, and don't think that Linux is whole generations behind Commercial Unixen. Linux Kernel is dramaticallly ahead in some areas and minorly behind in others. The only place it is dramatically behind is places where the computer you are running the OS on cost more than a half million dollars.
-- I am not a fanatic, I am a true believer.
Not to "troll" for my fav OS or whatever, but I've been playing with snapshots in FreeBSD-CURRENT for the last few days, and I must say that this is quite possibly the coolest filesystem technology I have ever seen.
/var/snapshots/snap1 /var". Becase of the way snapshots work, the snapshot must reside in the same filesystem that it contains.
In short, a snapshot is approximately equal to an image of a filesystem. To create a snapshot, you run a mount command like "-u -o snapshot
Now, once the snapshot is created, it can be treated like another filesystem. You can run fsck on it, dump it, or even mount it. The only difference is that within the snapshot, previous snapshots will appear as null files.
Basically, when you create a snapshot, you tell the filesystem that you want it's contents at the current time preserved, and the snapshot file is where it does this. Now, whenever said filesystem is modified, the modification is basically applied in reverse to extant snapshots. So, when a snapshot is first taken, it doesn't contain much information at first, but when you rm a file living in the directory, the file is saved into the snapshot. When you modify a file, deltas to reverse the change are saved to the snapshot.
This is extremely powerful used in the hands of a good sysadmin. Imagine your server that is backed up to tape every week. When someone comes asking for a file they clobbered or deleted by accident, you say "how old was the file?" - you know if they say "8 days", you have to go restore from tape, and if they say "2 days", you have to tell them that they are out of luck. Now imagine if a cron job was set up to take a snapshot once a day, and clear out old ones once a week. If they say "8 days", you still have to go fetch the tapes, but if they say "2 days", all you need is some mdconfig, mount, cp, and umount action to restore the file. How cool is that?
Snapshots essentially give your filesystems the "undo" capabilities that your editor has.
kernel 2.4 is not solid enough for me
to even start testing. if it doesn't
run on 2.2 then its not solid enough
for my needs. i don't want to have
to upgrade a kernel every 2-3 months
to fix a critical bug. reiserfs is
decent i use it on a few machines, but
ext2 is still the dominant filesystem
on my ~40 linux servers. most have
2 hours of battery backup and never
crash. so journalling isn't much of
an issue. the last power outage
that lasted more then 30mins that ive
experienced was back in 96 or 97 when
a tree branch broke a line and caused
most of the west coast to go to brownout/blackout state for 3-4 hours.