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Annoyed by LVM - Journal of Omnifarious

Oct. 12th, 2004

12:18 pm - Annoyed by LVM

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I tried to get LVM2 to do something it was supposed to be able to last night. I was trying to create a snapshot of the LVM volume that holds /. It then proceeded to cause every attempt to access / result in the program that did it freezing. This slowly froze every program on my system. It never did make the snapshot. I eventually ended up having to reboot.

I'm kind of annoyed by the whole thing. :-(

Current Mood: [mood icon] annoyed

Comments:

From:fusiongyro
Date:November 10th, 2004 09:48 pm (UTC)

LVM

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I started using LVM version 1 a while back. Then 2.6 came out, and with it LVM 2. There was a little detail they forgot to mention as I was upgrading to LVM 2… pvmove didn't work. Of course, pvmove actually was working, so there was nothing to mention—it just depended (and depends) on an ioctl supplied by the device mapper which wasn't implemented until (oh, say) two months ago. So, there was a pvmove out there on production systems, with no note in the documentation about dependence on an invalid ioctl, just a few mailing list posts from frustrated users saying "what does this 'unknown ioctl 9' message mean?" and the developers saying "yeah… sorry, pvmove depends on dev mapper and dev mapper doesn't do that yet."

I also ran LVM on my root for some time, because I hate repartitioning with a passion and hate running out of space on the root. When I was doing research trying to figure out why pvmove wasn't working, I discovered that it's a pretty well-known fact that running LVM on the root is a really bad idea, and how bad is sorely under-documented.

Overall, my experience with LVM, while punctuated by some excellent "ooh/ahh" moments, wasn't really worth the trouble of it all. The developers just don't seem aware of the gravity of the situation.
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From:omnifarious
Date:November 10th, 2004 09:52 pm (UTC)

Re: LVM

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I kind of agree that they don't seem to take what they're doing seriously enough. I'm not sure how to fix that either, other than starting another project that does the same thing with a promise that anything we release will be well tested, and all the functionality we promise will work will be documented.

I found the move to LVM2 to be pretty frustrating myself.

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From:fusiongyro
Date:November 11th, 2004 08:40 am (UTC)

Re: LVM

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I like the idea of LVM, especially for people like myself who just likes to run UNIX at home. I can't afford serious RAID but there's a problem I think is more compelling than LVM, because solving this other problem would (in a roundabout sort of way) also solve the LVM problem.

I want a real distributed filesystem. The qualities I want in it are: actual authentication, optional encryption, anonymous access, portability to (at least) Linux, FreeBSD, Windows and Mac OS X, distributed replication and failover, reasonable speed, and open-source. I looked into network and distributed filesystems recently, and it turns out that most of them offer authentication, either distributed replication or failover, or encryption, but the only one which has decent portability is NFS, which has the least features. In fact, of all the features I list here, portability is the least common. I'd forego Windows, but weirdly enough, most of these strange FS projects have a strange Windows driver, even if they don't port to FreeBSD.

Anyway, I'd find it much easier to get jazzed up over a project like that than LVM, because LVM is really just an annoyance compared to the network filesystem situation, IMO.
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From:omnifarious
Date:November 11th, 2004 08:51 am (UTC)

Re: LVM

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I'm working on a protocol layer on top of which one could build a decent secure distributed filesystem.

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From:fusiongyro
Date:November 11th, 2004 07:30 pm (UTC)

Re: LVM

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Where can I learn more?
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From:beastieb
Date:July 7th, 2005 06:31 am (UTC)

Re: LVM

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hi, i've partitioned the disk with only two partitions, one for the '/' partition, and one for the /boot. do you know how can i repartition the disk so that i have /usr /var as partitions too? i've tried to use resize2fs from the fedora distribution, but it can't run on itself, so i couldn't resize it. have you used some rescue cd with it? thanks
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From:fusiongyro
Date:July 9th, 2005 09:29 pm (UTC)

Re: LVM

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Hey,

You should probably try Knoppix, or some live CD which comes with the LVM tools. Barring that you might be able to make it work by copying crap to a RAM disk from your hard disk.

Fedora is crap, I would definitely not recommend running LVM with that.

When I was using LVM, I always made sure to leave some unpartitioned space around for futzing around. You probably should do that next time, too.

I don't know anything about resize2fs, because I used ReiserFS. the Reiser tools didn't have any trouble working on the filesystem while live. You should probably use that next time too.

You should email me directly, fusion at clanspum.net, if you need anything else. I don't check LJ very often for this kind of thing.

Best of luck. :)
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