[ovirt-devel] New SDM verb: SDM.copy_data

[Adam Litke]

Hi oVirt!

I wanted to take a moment to update you on a new storage verb we have
in vdsm called SDM.copy_data.  The purpose of this verb is to allow
copying of data between various endpoints* on hosts that are not
necessarily the SPM.  This will allow us in the future to spread the
load created by this data-intensive operation across multiple hosts
while providing a better user experience than the current SPM-driven
flow can.

Current status (Sprint 1):
 - Basic SDM.copy_data is merged to vdsm
 - We still use the SPM host for creating the destination disk and to
   serially copy all volumes.
 - The engine Move Disk flow is being adapted to use the new verb.
   Patches should be merged in the next day or two.
     https://gerrit.ovirt.org/#/c/61087/
 - New code paths must be activated by setting a config variable:
     "update vdc_options set option_value = true \
      where option_name = 'DataOperationsByHSM';"
 - Currently positive flows are implemented

Next steps:
 - Copy progress reporting in UI
 - Support negative flows (eg. lost contact with host)
 - Use this verb for live storage migration flows
 - Vdsm-side locking
 - Select a non-SPM host (when available) for copying

Farther out:
 - Support for copy in parallel
 - Implement other data path verbs (eg. wipe_volume, sparsify_volume)

-- 
Adam Litke