setAllMetadata called rbdImage.SetMetadata once per key, and each call opened and closed the RBD image on its own. On the CreateVolume path this meant the image was opened at least three times (the parameters map plus the clusterName and mounter keys), which is wasteful.

Open the image once at the start of setAllMetadata and issue all SetMetadata calls against that single handle, closing it via defer.

Apply the same change to the symmetric unsetAllMetadata, which had the identical open-per-key pattern.

Behaviour is unchanged: the same keys are set/unset, the same error messages are returned, and unsetAllMetadata still tolerates ErrNotExist.

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