Reliability of Journalling Filesystems Under Linux?

chrysrobyn asks: "Every write-up I see about journalling file systems under Linux discusses efficiency (embedded) or speed (desktop/server). Have any studies been done on reliability? I've used Linux since Slackware 96 (and kernel 2.0.0), and put it on 9 or 10 machines over the years (Slackware on x86 and Debian on PPC), but I've never strayed from ext2. Always, when the uptime gets high, 20-50 days, the filesystems start to get minor fsck errors. Not that I repair the system and expect it to stay live, I just use the fsck -n to help me decide when a repair is in order. Since the same thing has happened on a variety of hardware (386-PII and every interface in between and 601 and 750 processors with Apple hardware), I'm leaning on blaming the ext2 filesystem for these, the slightest of problems. I typically keep my servers up for as long as possible because 95% of my hardware problems have happened during resets and cold power-ups. It's time for my every-other-year rebuild of my personal server, with another on its way, so I was hoping to incite some anecdotal Slashdot conversation on the journalling file systems available for Linux. Personally, I'm most interested in hearing about the file systems supported under Debian stable for ease of administration for this machine which is a 5 hour drive away from home. I've been around the block a few times, so I'm not fearful of patching the kernel with better patches, but I'm respectful of the work the Debian assurance teams have done."

Comments

If you are fscking a live filesystem

[Pathwalker]

you have to expect some errors to show up from time to time, because the filesystem may change while fsck is running, and if so it will not be internally consistant.

Few links for you

[Rubbersoul]

Not knowing the answer to this myself I present to you a few links that may be helpful. Hope this helps.

This link has some good benchmarks of Ext2, ReiserFS and XFS.

And here is a fairly good news group discussion relating to what you are talking about.

/something/ is wrong here.

[Eivind]

ext2 is a quite stable fs. It is not journaling, so crashing at an inconvenient time can lead to an inconsistent fs, but other than that there is no reason why an ext2 fs should magically develop inconsistencies after 3-6 weeks of runtime.

You should be aware that if you are running fsck -n on the fs while it is mounted in rw-mode, then it can and will report inconsistencies which are not real, simply because the fs has changed between the passes in fsck, something which it does not expect.

For this reason, I suggest you try again with remounting the fs in ro-mode before running fsck -n. I am fairly sure you will find that your errors go away. Especially since you state this has happened on diverse hardware and presumably diverse kernels.

That said I would recommend going with a journaling fs for that extra safety that comes from never getting inconsistent even if the power goes out at the worst moment. ext3 and reiserfs are both good, my preference would be ext3 for the simple reason that it can be mounted as an ext2-fs, which means that you will be able to read it with any old rescue-disk or whatever. Reiserfs typically requires you to redo all your rescue-disks, and make sure that your backup-restore-scheme handles it rigth.

If the remounting in ro-mode does *not* make the reported errors in fsck -n go away, and you are somehow able to reproduce this, please report the bug to linux-kernel.

Ext3 vs ReiserFS

[DarkDust]

I don't know about XFS and other journalling fs's since I've only used ReiserFS and Ext3 so far.

My experience so far is that Ext3 is more reliable (read: repairable) than ReiserFS simply due to the fact that Ext3 is a kind of "extension" to Ext2, so you can just run the good old well tested and known to work fsck.ext2 on a Ext3 partition should it screw up.

But I have yet to see a Ext3 partition screwing up, I've set up several PCs and servers with Ext3 and it works fine, no single problem to date.

Unlinke ReiserFS. I have to admit, my only experiences with ReiserFS were about one and a half years ago or so, but at that time I had set up a home PC with ReiserFS and somehow I f***ed it up beyond all repair. I don't remember what I did then but I just got scared of ReiserFS :-)

On the other hand I have still another home PC, running SuSE Linux 7.2 updated to 7.3 with ReiserFS which just runs fine, and this is my home server, running 24-7.

So I guess until you don't do anything stupid like I did both ReiserFS and Ext3 are pretty reliable today, given their widespread use you would probably have heard of any major glitches/problems ;-) The decision whether to use on or another is more performance/religion-wise, IMHO :-)

Re:Ext3 vs ReiserFS

[GigsVT]

Well I can fill in your gaps on XFS. XFS has run flawlessly for me for over a year now, on a 1.9TB RAID volume. EXT2/3 seems to have rough edges in regard to large file systems, for example, by default mkfs will set aside 5% of your disk for root use. That's 97GB wasted! Another problem is that you need to specify -T largefile4 or it will try to create way too many inodes, taking forever to create the filesystem, or fsck if you ever need to.

XFS is a very mature file system, and file systems that are many TB work fine with its defaults. Performs more consistantly too. EXT2/3 was very sensitive to RAID stripe size, and things like that. Even setting the special stride option, you had to recreate the filesystem many times to make sure things worked right. XFS performed consistantly at any stripe size, with no strange dips in performance if boundaries didn't line up just right.

In all, if you are building a large RAID, I would go with XFS. For day-to-day use of 200GB or less on a single disk, EXT2/3 is fine. (You probably still don't want to let it waste 5% of the disk, that is such a retarded default, use -m 1 to help reduce it)

Re:There's more (thanks for crediting me)

[Per Wigren]

Yes, this is a known troll but I still want to comment on this particular line:

On other unices, crashes usually are caused by external sources like power outages. Crashes in Linux are a regular thing, and nobody seems to know what causes them, internally. Linux advocates try to hide this fact by denying crashes ever happen. Instead, they have frequent "hardware problems".

Crashes in Linux are NOT a regular thing, unless you want to be extremly bleeding edge and/or use NVidia's drivers and/or ALSA (at least up to 0.90rc5) on 2.4 with lowlatency- and preemptive-patches. Especially if the above stuff are used on SMP-systems.

My system used to crash (freeze) frequently (every 2nd or 3rd day).. But after I sold my GeForce4-card and got a Matrox G450 instead, and switched back to using OSS instead of ALSA (I've got a SB Live..), I've not had a single crash! It has been running for several months without a single reboot, and everything is super-stable! I've used it heavily every day, burnt more than 150 CD-Rs, been on Direct Connect and Freenet 24/7 etc.. That's despite I run the heavily patched 2.4.19-gentoo-r8 kernel, and my whole system (including the kernel) is compiled with gcc 3.2 "-march=athlon-mp -O3 -mfpmath=sse -pipe"..

So my conclusion is: Linux IS stable! Extremly stable! The cause of 99% of the "linux crashes!"-bullshit is because of NVidia's crap-drivers (fast but unstable) and drivers still not "preemtive"-safe (ALSA on SMP for example).. But those things are not used on servers anyway.

And about the "hardware problems": Yes, you DO get hardware problems MUCH MUCH more often on cheap PCs than on multi-million-dollar Unix-servers from Sun/HP/IBM.. Cheap PCs uses the cheapest-of-the-cheapest variant of all components to cut down the price. Expensive Unix-servers use expensive components and have a lot of redundancy, so you don't have to have downtime just because a CPU, a harddisk som RAM or something else failed.

No problems with Reiser

[inkfox]

I'm afraid you won't get much more than anecdotal evidence on this question. Here's mine.

We had a bad network adapter which would fail when other DMA devices were busy. This meant that whenever disk I/O was heavy, using the network adapter was likely to cause a complete system lockup. This took a while to diagnose as the problems took upward of two weeks to reproduce.

Despite the equivalent of having the power cable yanked randomly a dozen times when the machine was at its busiest, we never had a single problem with Reiser. The file which was being written to existed as the old version, and there wasn't even a lengthy fsck. Integrity was 100%.

Do not trust your fs

[jsse]

trust your backup.

Two cents from an old admin.

Do not trust your backup...

[V. Mole]

Test your backup. Not just once, but periodically.

Two cents from a (different) old admin.