Dell PowerVault ML6000 - Manual (Page 11)

PowerVault ML6000 SCSI Reference Guide 1
SCSI Command Support
Device Model
The Dell™ PowerVault™ ML6000 tape library supports both a Media Changer device (device type 08h) and
a Controller device (device type 0Ch). This approach is used primarily to aid initialization and discovery for
the servers in conjunction with the library’s Logical Library model. In addition, the Controller device model
facilitates continued use of Host Registration Services (HRS) functionality, which uses private (externally
undocumented) commands and vendor unique parameters. In the case of a PowerVault ML6000 without
Data Appliance (DA) blades, there is no Controller device; the tape drives provide access to the Media
Changer devices
This device model approach works by having the Controller (typically at LUN 0) respond to all commands,
and the Logical Libraries (Media Changers) respond to other assigned LUNs (or Targets if on the SCSI
port). This approach allows an Initiator (Host) to issue a Report LUNs command to the Controller to retrieve
a listing of all available logical units on that port. For systems with Fibre Channel (FC) ports, this is an
advantage as there are large number of possible logical units to search. (In the case of a PowerVault
ML6000 without DA blades, this command should be issued to the tape drives.)
For a tape library with DA blades, this model can be extended to report the number of available tape drives
as well.
For all systems except the PowerVault ML6000 without DA blades, it is possible to define a Media Changer
at LUN 0 and the Controller at a different LUN. For a PowerVault ML6000 without DA blades, the Media
Changer(s) is always found at LUN 1, and the tape drive or drives are found at LUN 0.
Note that the Controller device is not a pure Controller device, in that it does not support all the mandatory
commands defined by SCC, but this is an accepted industry practice established by vendors of bridges and
routers.
Additional commands and parameters supported by the Controller LUN (such as Maintenance In) are for
use by Host Registration Services software, and are not included in this manual.
Note
"DA blade" is a generic term used in this manual to describe a number of
possible types of input/output blades, including FC-FC, FC-SCSI, and possibly,
in future, iSCSI-SAS or other combinations.