We have two distinct implementations here. The version for
StorageLevel.DISK is generic enough to work for StorageLevel.MAPPED, and
will guarantee consistency with reader implementation (which is already
shared across StorageLevels).
JIRA: CONTROLLER-2100
Change-Id: I3e9a5c8a72be766431e5cb527cae1f4809964dd7 Signed-off-by: Robert Varga <robert.varga@pantheon.tech>