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Previous versions of lvm will not obey the restrictions imposed by the new system_id, and would allow such a VG to be written. So, a VG with a new system_id is further changed to force previous lvm versions to treat it as read-only. This is done by removing the WRITE flag from the metadata status line of these VGs, and putting a new WRITE_LOCKED flag in the flags line of the metadata. Versions of lvm that recognize WRITE_LOCKED, also obey the new system_id. For these lvm versions, WRITE_LOCKED is identical to WRITE, and the rules associated with matching system_id's are imposed. A new VG lock_type field is also added that causes the same WRITE/WRITE_LOCKED transformation when set. A previous version of lvm will also see a VG with lock_type as read-only. Versions of lvm that recognize WRITE_LOCKED, must also obey the lock_type setting. Until the lock_type feature is added, lvm will fail to read any VG with lock_type set and report an error about an unsupported lock_type. Once the lock_type feature is added, lvm will allow VGs with lock_type to be used according to the rules imposed by the lock_type. When both system_id and lock_type settings are removed, a VG is written with the old WRITE status flag, and without the new WRITE_LOCKED flag. This allows old versions of lvm to use the VG as before.