[Users] SIMFS users

[Maxim Patlasov]

Hi,

On 08/04/2015 12:51 AM, Bosson VZ wrote:
> Hello,
>
> yes, we have 200+ containers all running on top of simfs in clusters. Most of
> the limitations of simfs mentioned above are not a problem to us as we use
> clustered LVMs on top of DRBD storage. Every container has its own file-system
> sitting on an LVM block device. This layout is universal for our OpenVZ and
> KVM guests (where a raw block device is passed to the guest). Different
> containers use different file-systems (ext4, xfs, nfs, ...), some containers
> share part of their file-system hierarchy with others in the cluster using
> ocfs2/gfs clustered file-systems. On non-cluster hosts, we sometimes use host-
>> guest bind-mounts as the way to share some data. Thanks to DRBD, live
> migration is also possible with minimal downtime.

The solution you described looks very interesting. How do you reclaim 
unused disk space from container to host system? More specifically: 
suppose, at the moment of creation of a container you devoted 100GB LVM 
block device for that container; later on you decided that 10GB would be 
enough for it; what do you do to return those unused 90GB back to the 
host (or to other containers)? I guess the only way is to fully shutdown 
the container, shrink its filesystem, then shrink LVM block device, then 
start it up again.

>
> The bossonvz libvirt driver at the moment only supports simfs (as that's what
> we are using nowadays).
>
> Is it somehow possible to use ploop in a cluster and share the virtual file-
> system between hosts?

You can keep ploop image files on a shared storage if its client 
filesystem is FUSE-based. For other filesystems more work needed, but it 
must be doable.

>
> How can host->guest bind-mount be achieved without simfs?
>

The same way as for simfs: "mount --bind /shared_space 
/vz/root/101/mnt"? It shouldn't matter whether mount-point 
"/vz/root/101" came from simfs or from ploop. Am I missing something 
obvious?

Thanks,
Maxim