> Fair enough, I understand one needs to use a different CM id. For the IB
> case I was thinking of avoiding APM (since that is limited to a device
> -isn't that so?).

APM is limited to a single device, as is memory registration, CQs, PDs, SRQs, 
etc.  Migration between devices requires entirely new memory registrations, the 
use of different lkeys/rkeys, and new CQs.  There's no guarantee that the HW 
devices support the same features - registration size, QP size, CQ size, etc.

> Is PD device specific? Couldn't one reuse the same CQs and MRs, even
> though the QP is different? Of course only one QP would be active at any
> time.

You can only reuse the resources if you limit yourself to the same device.

Supporting migration between devices requires a higher level abstraction which 
hides the internal RDMA device details.

HA itself likely requires more than simply establishing a new connection.  You 
may need to resolve the addresses again, to determine where to migrate to, plus 
obtain new path records.  Any app that wants full HA capability really needs to 
be able to handle a connection failing completely and establishing a new one.

- Sean
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