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The LUN is not the only way to identify a logical unit. There is also the SCSI device ID, which
identifies a logical unit uniquely in the world. Labels or serial numbers stored in a logical
unit's storage volume often serve to identify the logical unit. However, the LUN is the only
way for an initiator to address a command to a particular logical unit, so initiators often
create, via a discovery process, a mapping table of LUN to other identifiers.
There is one LUN which is required to exist in every target: LUN 0. The logical unit with LUN
0 is special in that it must implement a few specific commands, most notably report LUNs,
which is how an initiator can find out all the other LUNs in the target. LUN 0 does not
provide any other services, such as a storage volume. Many SCSI targets contain only one
logical unit (so its LUN is necessarily 0). Others have a small number of logical units that
correspond to separate physical devices and have fixed LUNs. A large storage system may
have up to thousands of logical units, defined logically, by administrative command, and the
administrator may choose the LUN or the system may choose it.
Figure 8-3
LUM Mappings in Storage Architecture
Volumes are then allocated out of the storage pool and are mapped to LUN which can be
accessed by a host system. In Figure 8-3, a LUN can be accessed by cluster with two or
more hosts via iSCSI. Or can be accessed by MPIO to provide HA (High Availability)
architecture and increase the access bandwidth. The snapshot volumes can also be
mapped to a LUN. The same, the read-only snapshot LUN can be read by the host, and the
writable snapshot LUN can be read/write.
Summary of Contents for XCubeSAN XS5224D
Page 71: ...SANOS User Interface 49 nnnnn RPM Power Supply Local PSU n status Reset to Default Yes No...
Page 99: ...System Settings 77 Figure 6 14 System Information...
Page 315: ...Monitoring 293 Figure 13 5 Hardware Monitoring...
Page 327: ...Support and Other Resources 305 Figure 15 1 Download Service Package in the SANOS UI...
Page 331: ...Support and Other Resources 309...