Dizwell Informatics

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Fed Up, Zed Up?

Spot the problem shown in these two screen grabs:

You will immediately notice from the second screenshot that version 0.6.5.8 of whatever it is which happens to have been screenshotted only supports up to 4.8 kernels, whereas the first screenshot shows that a Fedora 25 installation is using kernel version 4.9. Clearly that Fedora installation won’t be able to run whatever is being referred to in the second screenshot.

So what is it that I’ve taken that second screen shot of? This:

Ooops. It happens to be a screenshot of the current stable release number of the world’s greatest file system for Linux.

Put together, and in plain English, the combination of the two version numbers means: I can’t install ZFS on Fedora.

Or rather, I could have done so when Fedora 25 was freshly installed, straight off the DVD (because it ships with a 4.8 kernel, so the 0.6.5.8 version of ZFS would have worked just fine on that). ZFS on 4.8-kernel-using-Fedora 25 works fine, therefore.

But if I had, say, copied 4.8TB of data onto a freshly created zpool and then updated Fedora, I would now not be able to access my 4.8TB of data at all (because the relevant ZFS kernel modules won’t be able to load into the newly-installed 4.9 kernel). Which sort of makes the ZFS file system a bit less than useful, no?!

Of course, once they release version 0.7 version of ZFS (which is currently at release candidate 2 state), then we’re back in business -because ZFS 0.7 supports 4.9 kernels. Unless Fedora go and update themselves to using kernel 4.10, of course… in which case it’s presumably back to being inaccessible once more. And so, in cat-and-mouse fashion, ad infinitum…

But here’s the thing: Fedora is, by design, bleeding edge, cutting edge… you name your edge, Fedora is supposed to be on it! So it is likely to be getting new kernel releases every alternate Thursday afternoon, probably. What chance the ZFS developers will match that release cadence, do you think… given that their last stable release is now 4 months old?

About zilch I’d say. Which gives rise to a certain ‘impedance mismatch’, no? Try running ZFS on Fedora, it seems to me, and you’ll be consigning yourself to quite regularly not being able to access your data at all for weeks or months on end, several times a year. (Point releases of the 4.x kernel have been coming every two or three months since 4.0 was unleashed in April 2015, after all).

It strikes me that ZFS and Fedora are, in consequence, not likely to be good bed-fellows, which is a shame.

Perhaps it is time to investigate the data preservative characteristics of Btrfs at last?!

Incidentally, try installing ZFS on a 4.9-kernel-using-Fedora 25 whilst the 0.6.5.8 version of ZFS is the latest-and-greatest on offer and the error you’ll get is this:

The keywords to look for are ‘Bad return status’ and ‘spl-dkms scriptlet failed’. Both mean that the spl-dkms package didn’t get installed, and the net effect of that is the ZFS kernel modules don’t get loaded. In turn, this means trying to issue any ZFS-related commands will fail:

Of course, you will think that you should then do as the error message tells you: run ‘/sbin/modprobe zfs’ manually. It’s only when you try to do so you see the more fundamental problem:

And there’s no coming back from that. 🙁

No practical ZFS for a distro? That’s a bit of a deal-breaker for me these days.

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