[Scst-devel] LUN replacement

[Consus <co...@gm...>]

Hello folks,

I'm trying to implement Active/Passive. The problem is that my block
device that I want to export to initiators cannot be present on both
nodes at once. So I want to use the following technique:

    - Active
        
        1. Create SCST device dev0 (vdisk_blockio)
        2. Add dev0 to device groups
        3. Create SCST device dev0_null (vdisk_nullio)
        4. Because prod_id, t10_vend_id, usn, etc are generated based on
           device's name (dev0_null) I have to manually set these
           parameters to match dev0's ones
        5. Add dev0_null to dev0's groups

    - Passive

        1. Create SCST device dev0_null (vdisk_nullio)
        2. Because prod_id, t10_vend_id, usn, etc are generated based on
           device's name (dev0_null) I have to manully set these
           parameters to match dev0's ones
        3. Add dev0_null to dev0's groups

If I want to failover:

    - Active

        1. Change Active to Unavailable (Bart mentioned that
           Transitioning is not handled very well by some OSes)
        2. Replace dev0 with dev0_null
        3. Remove SCST device dev0
        4. Shut down my wannabe-clustered block device
        5. Change Unavailable to Passive

    - Passive

        1. Bring my wannabe-clustered block device
        2. Create SCST device dev0 (vdisk_blockio)
        3. Add dev0 to device groups
        4. Replace dev0_null with dev0
        5. Change Passive to Active

Am I doing it right?