Other Considerations - EMC DL3D 1500 Administrator's Manual

Other considerations

not function properly when incorrect combinations of library and
tape drive types are specified. When they fail, it may not be obvious
that it is due to an invalid combination.
Note: EMC recommends creating virtual tape library and drive combinations
that are formally supported with real physical libraries/drives. See the EMC
Support Matrix for the latest supported combinations.
The number of slots defined for a particular virtual tape library is not
limited to the number found in the physical tape library it is
emulating; it is limited by the number supported by the backup
software application.
When you create tape cartridges, they are spread across the storage
LUNs in a round-robin fashion. This maximizes the performance by
spreading the I/O load across multiple LUNs. If tape cartridges are
created individually (or only a few at a time), they can potentially be
allocated to the same LUN, which results in poor overall (aggregate)
throughput.
You can customize the cartridge size, but it cannot exceed the
capacity of its physical equivalent. This ensures that the compressed
data stored on a virtual tape cartridge will fit on a physical tape once
it has been decompressed and then recompressed by the physical
tape drive. You cannot create tape cartridges larger than their
physical equivalents on the DL3D 1500 and DL3D 3000. A size of 100
GB has been found to be a good minimum virtual cartridge size.
If you use the Path-to-Tape feature, create virtual tape cartridges of
the same type as the physical tape used in the Physical Tape Library
(PTL), if possible, or the same virtual cartridge type used in the EDL.
If your PTL uses a tape type that the DL3D does not emulate,
configure the virtual tape cartridges as LTO-1.
The DL3D 1500 and DL3D 3000 emulate a number of
industry-standard library and tape drive types. These appliances
support the use of multiple virtual libraries and tape drives
simultaneously. To address backup bottlenecks commonly seen with
shared devices, use one of the following two approaches:
Create a library and tape drives for each backup host's exclusive
use. This ensures the best possible performance by removing
delays inherent with shared tape drives.
Configuring and Managing Virtual Tape Libraries
Introduction 57