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Chapter 2 HPSS Planning
HPSS Installation Guide September 2002 101
Release 4.5, Revision 2
The STK RAIT PVR cannot be supported at this time since STK has not yet made RAIT
generally available.
In Table 2-4:
• Tape Type is the specific type of media to which the values in the row apply.
• Media Block Size is the block size to use in the storage class definition. For tape, this will
be the size of the data blocks that will be written to tape. Note that for tape devices, the
Mover configuration does not contain the media block size. The selected block size is set
on a per physical volume basis at the request of the Tape Storage Server. This value may
have a significant impact on data transfer performance, as for most tape devices each
input/output request must be for the media block size. If a large block size is used for
relatively small write requests, space may be wasted on the tape if the drive can not
compress the unused portion of the data blocks.
• Blocks Between Tape Marks is the number of media blocks to be written between tape
marks, to be set in the storage class definition. A relatively small value has the benefits of
lower access time for position to the middle of a file (the start of a file will be just after a
tape mark). Small values have the penalties of poorer media utilization and a performance
penalty when writing tapes. Since files are usually read in their entirety, and since modern
tape controllers are designed to stream data to tape, larger values of the Block Between
Tape Mark parameter are recommended.
• Estimated Physical Volume Size is the estimated size of the physical volumes to be set in
the storage class definition. These values are based on the expected media to be used with
the specified type. In somecases, different length tape media may beused, which may have
an effect on the estimated size for a given physical volume (e.g., regular or extended length
3480/3490 format cartridges). Note that the values listed do not take into account any data
compression that may be performed by the tape drive. Also note that this value is for
informational purposes only and does not effect the amount of user data written to a tape
volume by the Tape Storage Server. The server fills each tape Virtual Volume and the
amount of data written to the tape varies with the compressibility of the data.
2.9.2 Storage Hierarchy
Each HPSS file is stored in a single storage hierarchy consisting of an ordered list of storage classes.
A storage hierarchy can have up to 4 levels starting with level 0. The highest level is always level 0
and the lowest possible level is level 4. For example, a level 0 storage class could be fast disk while
a level 4 storage class could be a slow, large capacity tape system. The SSM provides operational
capabilities to define storage hierarchies. A storage hierarchy is identified by a storage hierarchy ID
StorageTek Redwood 256 KB 512 50 GB
StorageTek Timberline 64 KB 1024 800 MB
Table 2-4 Suggested Block Sizes for Tape
Tape Type Media Block Size
Blocks Between
Tape Marks
Estimated Physical
Volume Size