[sheepdog-users] vdi and dynamic allocation

[Valerio Pachera]

2012/12/14 Liu Yuan <namei.unix at gmail.com>:
> Yes, it is possible for us to support shrink the image offline. If this
> is desired, we can implement it.

I think it may be a good way to optimize the cluster.
Think of this scenario: you sell a virtual private server (vps) with X
G of vdi space.
The vps administrator do something wrong (like too many backups) that
will use lot's of space.
Later he will remove the unnecessary data.
We have a lot of space allocated by the vdi of this vps that can't be
used by other vdis in the cluster.

The word 'shrink' may be misunderstood like 'to reduce the virtual
space of a disk'.
So it may be better use something else like 'optimize' or 'free_allocated"

There may be two ways to implement the shrinking:
- explicit command like 'collie vdi optimize <vdiname>
- or as an option of the cluster.

In the first case, the "clean up" is done manually by the cluster
administrator, disk by disk.

In the second case, sheep dog it self is going to take care of the
cleaning up of all the vdis.
The I/O of removing unused chunks may be done with a very low priority
so to not impact the cluster performance.
I do not know if the 'optimize' option may be given when we
create/format the cluster, or later by a command.
That probably depends on how sheepdog works internally.