On Mon, Apr 19, 2010 at 11:09:17AM +0100, Daniel P. Berrange wrote:
On Sun, Apr 18, 2010 at 10:55:04PM +0200, Matthias Bolte wrote:
I'm currently implementing the storage driver for ESX and have a mapping problem.
libvirt storage pools can be either running or inactive just like the domain. ESX is a bit different here. A datastore is always active. It can be inaccessible, e.g. if an NFS is mounted as datastore but the NFS server went unreachable. I discussed this with Daniel on IRC and he summarized it like this:
<DV> they are defined, the system knows them, but they are not available for use
The question is, what should the ESX driver do with inaccessible datastores?
Option 1: They could just be represented as inactive storage pools, but libvirt's semantic for inactive storage pools includes that the user can start an inactive storage pool. That's not possible for an inaccessible datastore, so the driver would report an error if a user tries to start an inaccessible storage pool.
I don't think this is a good match, because 'inactive' implies that the system hasn't even connected to the NFS server.
Option 2: Just ignore inaccessible datastores and make the ESX storage driver to pretend that they don't exist. But this would hide information from the user.
Agreed, hiding info is not good.
Option 3: Extend libvirt's API for inaccessible storage pools.
This is the only one left !
IMHO, the 'inaccessible' data store is active. A little noticed fact is that the storage pool state is actually more than just a boolean. At least in the public API we define
typedef enum { VIR_STORAGE_POOL_INACTIVE = 0, /* Not running */ VIR_STORAGE_POOL_BUILDING = 1, /* Initializing pool, not available */ VIR_STORAGE_POOL_RUNNING = 2, /* Running normally */ VIR_STORAGE_POOL_DEGRADED = 3, /* Running degraded */ } virStoragePoolState;
THe 'BUILDING' state is to indicate cases where the storage is being constructed in some way.
The 'RUNNING' state is the normal runtime state.
The 'DEGRADED' state indicates that it is fully operational, but in a degraded state. eg, one of the members of a RAID array failed, or one of the SCSI paths failed, etc.
The DEGRADED state doesn't exactly map to your NFS example though because in case of a non-responsive NFS server, you can't use the pool.
Thus I'd suggest just adding a 5th option
VIR_STORAGE_POOL_INACCESSIBLE = 4 /* Running, but not accessible */
Agreed; I didn't read your response before I posted mine. This sounds like the right way to to it. Dave