Loopback mounts do not work with local provider, use directory storage

[Stuart Bishop]

The swift-storage charm needs to use loopback mounts, but these don't appear to work under LXC unless you tweak the default templates per http://osdir.com/ml/lxc-chroot-linux-containers/2013-01/msg00036.html

The charm fails when it tries to run losetup.

# losetup --find /etc/swift/storagedev1.img
losetup: Could not find any loop device. Maybe this kernel does not know
       about the loop device? (If so, recompile or `modprobe loop'.)
# modprobe loop
FATAL: Could not load /lib/modules/3.11.0-13-generic/modules.dep: No such file or directory

[Curtis Hovey (sinzui)]

This appears to be a known issue:
    http://comments.gmane.org/gmane.linux.kernel.containers.lxc.general/4537
    http://askubuntu.com/questions/141552/creating-volume-group-in-nova-volume-juju-charm

[Stuart Bishop (stub)]

I doubt there is anything to do at the Swift charm end,, flagging as INVALID there.

[Stuart Bishop (stub)]

Can the Swift charm make use of alternative storage that doesn't require a loop device?

[Martin Pitt (pitti)]

Swift can definitively do that. http://www.piware.de/2014/03/creating-a-local-swift-server-on-ubuntu-for-testing/ describes what I did for that, and http://people.canonical.com/~pitti/scripts/setup-swift.sh is the script to run in a container to set up everything. The important bit here is to set "mount_check = false" and "devices = /srv/swift/" (or whichever other directory you use) in object-server.conf.

[Martin Pitt (pitti)]

BTW, I see little value in using a loopback mount even for "real" clouds; that will still be QEMU, so a directory storage will be at least equal to, or even faster than an image file through loopback.

[Heather Lanigan (hmlanigan)]

It'd be nice to have this. I ran into the same issue. I'm trying to use the Glance Simplestreams Sync charm with the openstack-novalxd bundle. Deployed swift for it and ran into this problem.

Or could the Glance Simplestreams Sync charm using other container options as well?

[Drew Freiberger (afreiberger)]

Adding another +1 to wanting swift-storage to allow for directory/mountpoints in swift-storage charm's block-devices as we can use with ceph storage.

Odd, but important use case:

bcache bypass using /dev/loop0 to mount the backing store (8k offset, losetup -o 8192 /dev/loop0 /dev/$bcache_backing_device) and then mounting /dev/loop0 to /srv/node/bcache0 where bcache lived before.