[Bug 1028718] [NEW] nova volumes are inappropriately clingy for ceph

[Paul Collins]

Public bug reported:

I've been doing a little work with nova-volume and ceph/RBD.  In order
to gain some fault-tolerance, I plan to run a nova-volume on each
compute node.  However, a problem arises, because a given nova-volume
host only wants to deal with requests for volumes that it created.

This makes perfect sense in a world where nova-volume hosts create
volumes in LVM and export them over iSCSI.  It makes less sense in a
Ceph world, since the volumes live in the ceph cluster, and their
metadata live in the nova database.  But if the wrong nova-volume goes
away, some of my volumes become arbitrarily unusable.

I've hit upon a workaround that seems to work so far, although I'm not
sure if it's supposed to.  I am running each nova-volume on the various
hosts with an identical --host flag.  When running in this setup, rapid
volume creation, deletion and attachment requests are splayed nicely
across the nova-volume instances.

(A less brutal hack might be to teach nova-volume to call into the
volume driver to check if it has its own notion of what the host flag
ought to be -- the RBD driver, for example, could construct a string
such as "ceph:67670443-07ad-4ce3-bdb8-75e9a14562f9:rbd" by probing the
Ceph cluster for its fsid, which ought to be unique, and then appending
the name of the RADOS pool in which it is creating RBDs.)

** Affects: nova (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: canonistack

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Title:
  nova volumes are inappropriately clingy for ceph

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