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10
FC/SCSI Tape Pipelining
10-5
Dynamic Target LUN Discovery and LUN Mapping
Target discovery is not aware of device type or available LUNs on the
discovered target.
LUN Discovery
A maximum of 32 devices can be discovered or configured
unidirectionally per I/O pair. Available bandwidth should be
considered for concurrent operation of the drives.
As targets are discovered, those targets will be queried for available
devices via LUN discovery. A configurable number of LUNs
(maximum of 32, default is 8) will be attempted to be discovered for
each discovered remote target. These devices will be mapped on the
Edge target LUN field with the dynamic LUN mapping rules. LUN
discovery will filter remote LUNs based upon the device type field in
the inquiry response. Only device types of tape and changers will be
added to the host LUN table. LUN Discovery is only done to newly
discovered remote targets.
LUN Refresh
Remote targets will be scanned for newly available LUNs whenever
the target Edge is rebooted or the user issues the “refresh” command
via the ttag user interface. If any new LUNs are discovered, those
LUNs will be added to the host LUN table, if an open host LUN field
is available. Existing LUNs already discovered to any remote targets
will not be rescanned. LUN refresh will not remove a remote device
which is no longer available.
Dynamic LUN
Mapping
The Edge target will discover, via Edge initiator target discovery,
available remote targets. The Edge target will map discovered targets
based upon WWNs on a first learned basis. The discovered targets
will fill the Edge target LUNs from lowest (1) to highest (x). The
mapped LUN will be bound to the associated WWN and any change
in remote target portid will be dynamically learned. The WWN and
associated Edge target LUN will also be stored onto disk which will
provide consistency on the Edge target LUN mapping across resets
and power downs.
Static LUN Mapping
The Edge target may be configured for a specific Edge target LUN to
be bound to a designated remote target WWN. If a remote target is
statically configured, all LUNs to be mapped to that remote target
must be statically configured and should be mapped consecutively
from lowest to highest. Any Edge target LUN not statically
configured will be discovered via dynamic LUN mapping.