[systemd-devel] cannot start swap unit on lvm

[Damien Robert]

Alexey Shabalin  wrote in message
<CAEdvWkQTe1rZ=+ARtOm3HFr6rc8Qgvbf2MGqfX44k+erjHpFkg at mail.gmail.com>:
> [Swap]
> What=/dev/disk/by-uuid/a8ce6981-1afd-4af6-8783-784b3c7a7d64
> systemctl start
> "dev-disk-by\x2duuid-a8ce6981\x2d1afd\x2d4af6\x2d8783\x2d784b3c7a7d64.swap"
> cannot activate swap, error by timeout.
> but swapon "/dev/disk/by-uuid/a8ce6981-1afd-4af6-8783-784b3c7a7d64" fork fine.

This looks a lot like the bug I had here
https://bugs.archlinux.org/task/31306

I talk about a timeout for mounting /home, but mounting swap also
timeouted.

As you can see on the bug report, I have a similar setup to yours: swap on
lvm, and referencing to it by the uuid. A possible explanation given by the
arch maintainer was that the /dev/by-uuid links were not made, explaining
why systemd could not find the filesystem. The swapon and mount works
because they don't rely on these symlinks whereas systemd work. So if this
is the case it would be more a udev problem than a systemd one.

This happened with kernel 3.4.9, upgrading to 3.5.3 solved it (and
strangely going back to 3.4.9 did not give back the problems, so I could
not investigate further and the conditions for the bug to produce look to 
be quite unstable).

> Sorry, i know that swap on lvm bad idea, but ...

I use lvm for my /, /boot, /home and swap partition and I really regret it.
- Since grub2 went from 1.99 to 2.00, the lvm code changed, and the
corresponding core.img does not longer fit in my 31.5kiB MBR gap.
- I got the bug you mentioned
- Currently with kernel 3.5.3 using ArchLinux the lvm detection fails in
  the initrd (the dm_mod module takes longer to load, so there is a race
  such that lvm vgchange --sysinit -a y sometime do not find the lvm
  partitions): 
  https://bugs.archlinux.org/task/30966?string=lvm
- it slows down the boot
  http://freedesktop.org/wiki/Software/systemd/Optimizations
Next time I reinstall my computers I'll go with btrfs subvolumes instead!