Resource Management
8.
Resource Management
8.1
Introduction
The physical resources of a RLS tape library may be sub-divided for multiple purposes
by allocating tape drives, I/O ports and storage locations to specific partitions. The
Handler (the libraries robotics) is a shared resource that cannot be dedicated to any
single task.
Except for cleaning cartridges, resources cannot be shared between two enabled
partitions. A logical library partition is enabled when its Mode value is set to Library,
Sequential, Recycle or Dual Bin.
A good example of dedicated resources is that of a Sequential tape drive and its
allocated storage locations. A sequential tape drive looks to the host computer as a
single tape drive with an operator supplying it with tapes. A host backup application
that is not aware of tape libraries, can simply write its backup data to the drive until
the tape becomes filled. It then causes the tape to be rewound and ejected from the
drive. The changer can then automatically insert the next tape needed to continue the
backup operation. The host application is completely unaware of how the next tape
gets inserted into the drive as well as where the tapes come from and go to.
For this example to succeed in an automated tape library, one or more tape cartridges
must be dedicated to the Sequential backup performed by the drive. To the changer
(referred to as the Medium-changer in the SCSI specifications), the tape drive and a
group of cartridges are reserved for that task. These dedicated resources cannot be
used for any other purpose. If this example is all that is required of the changer, then
only a single drive is installed and all of the cartridges are dedicated to this single
task.
However, the RLS libraries are much more flexible than our example. They can
perform three modes of sequential backups on multiple tape drives for multiple host
systems while simultaneously running multiple random logical library operations
with other tape drives and cartridge locations. Before the library is put to use, you
have to decide how it is to be used and then allocate the available resources to meet
the requirements. This chapter will deal with this task.
8.1.1
Element Addresses
From the SAS (or Fibre Channel) interface, cartridge locations are identified by their
Element Address if the partition type is Library. Unlike the permanent and absolute
Location designators, each SCSI element address is assigned by the RLS. Element
addresses are 16-bit unsigned integers (0–65535). All elements of the same type (e.g.
Storage) are numbered consecutively. Element addresses are only assigned to
locations within a logical library partition (see Chapter 9).
8-1
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