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I am wondering if ext4 is safe to use on my servers. But I've heard so much FUD about it that I am concerned.

Our system could lose some data, and it would not be too big a deal. Even a full days worth of data would not ruffle too many feathers. And our system could most definitely benefit from delayed writes.

That said, a full file system restore from backup would take days and be unacceptable.

Any experience or informed opinions on the subject out there?

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6 Answers 6

up vote 12 down vote accepted

Honestly, I'd hold off on ext4 right now for production use.

There are other options if you're running into real performance problems with the filesystem (and I can understand that situation, at my last job we had performance limitations in an application due to ext3). Depending on your chosen distribution, you might be able to use jfs, xfs, or reiserfs. All three will generally outperform ext3 in different ways, and all three are much more tested and stable than ext4 right now.

So, my recommendation would be multiple parts. First, investigate thoroughly to make sure you're optimizing in the right place. Test your application on different filesystems and ensure that the performance is improved enough to make a filesystem change valid.

Also, depending on your application, adding more RAM might improve performance. Linux, by default, will make use of any RAM that isn't committed to applications as disk cache. Sometimes having a few GB of "unused" RAM can have a significant performance increase on boxes with heavy disk activity.

Finally, what's your timeline requirement here? If ext3 wasn't cutting it and I had to build a machine with a different filesystem today, I'd probably use xfs or jfs. If I could push it off for 6-8 months, I'd probably wait and see how ext4 has shaped up.

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1  
Thanks for the empathetic feedback. :) No, I am in no rush. Have already added some GB of RAM which has worked wonders. I'm just keeping my eye on all potential performance bottle necks at this point and learning about what my options are. My biggest worry is a sift in usage patterns or a new application requirement could change everything for me. "Be prepared" or whatever that motto is. Ext4, on paper, seems like a viable option. I'd hate to discount it because of competing file system seeded FUD. Hence my question. –  Stu Thompson May 4 '09 at 15:29

I've found that feedback from http://web.luchs.at very interesting. They used ext4 on Debian lenny based servers and that seems to work great !

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Thanks for the links. If you could, please quote from it in your answer, make the links more individually definable, and I'll give you a cookie :) –  Stu Thompson Apr 30 '09 at 19:09

That said, a full file system restore from backup would take days and be unacceptable.

Then stick to ext3, as a bonus, any slob with a Fedora USB key can mount your drive if it comes to that.

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Is there a risk that I could loose the entire file system, then? –  Stu Thompson Apr 30 '09 at 10:51
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There is always a risk. The number of people running ext3 vs the number of people running ext4 dictates that ext4 has received less real world testing. –  Dave Cheney Apr 30 '09 at 10:55
    
Without supporting information, your last comment here sounds like FUD. Of all the criticism of ext4 I have heard, total volume loss is not one of them. If you know of such events then please put us in the know. This is the kind of concrete criticism I am looking for. –  Stu Thompson Apr 30 '09 at 19:05
    
Not FUD, just being practical. ext3 has been standard in distros for many years, ext4 was only merged in 2.6.28 en.wikipedia.org/wiki/Ext4. Do you use 1.0 products ? –  Dave Cheney Apr 30 '09 at 22:31
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I've read the wiki. There are some solid 1.0s, there are some shoddy 7.0s. I hear the complaints, but don't want to be paralyzed by fear. FUD is vague and fuzzy, like our answer, which is essentially "New == Too Risky". I'm in search of specifics. Details! –  Stu Thompson May 4 '09 at 15:46

ext4 is still very new. The conservative approach would be to use ext3 or something with known reliability characteristics. I'd recommend ext4 at this point only for systems where reliability isn't critical, or where the new features in ext4 dramatically outweigh the risk of data loss.

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Unless you are worried about hitting the limits of ext3 I wouldn't bother. While ext4 offers a number of improvements, most of them are not aimed at regular users.

In general it is safest to go with the most mature technology that will comfortably fit your needs to the foreseeable future. If you have no need for the new fancy things, then you are adding risk (however small) for no benefit.

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I am worried about hitting the limits. Not today, not tomorrow, but the day after. I'm just suspicious of unsubstantiated naysayers. (E.g.: My prime function is Java coding, and yet to this day people tell me Java is dead and support it with junk like "it is too slow" (has not been true for a long while) and "it is too old" (huh?)) Basically, I am comfortable with risks I understand, and to do that I need to know the specifics. Gosh...hope that made sense to you! –  Stu Thompson May 4 '09 at 15:51

Certainly Ubuntu 9.04 (jaunty) is still working out the bugs of ext4 in their version of kernel 2.6.28. Some bugs appear to only be in the ubuntu kernel rather than the mainline, but that indicates that if you have a non-mainline kernel you may run into similar troubles.

This page is a search of issues with ext4 that could be worth a browse. One current (6th May 2009) serious issue that causes the kernel to lock up is issue 330824. And a previous issue (now fixed) involved data loss. But I have not heard of any loss of the entire file system, and I think it would be big news if it was happening.

So I would say it is not entirely ready for prime time. If you really need it, then it may be worth setting up a test server to play with it. For the time being I would stick with the mainline kernels, and measure the performance gain - if the gain is dramatic and stress testing does not show up any problems then it might be worth trying it ...

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Now that was exactly the kind of specifics I was after. Thanks, mish. –  Stu Thompson May 6 '09 at 21:52

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