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3.10.1.8. Maximum VVs to Write (tape only)
This parameter restricts the number of tape VVs, per Storage Class, that can be concurrently written
by the Core Server. Its purpose is to minimize the number of tape mounts and to limit the number of
tape VVs being written, to prevent files from being scattered over a number of tapes. The number of
tape drives used to write files in the Storage Class will be limited to approximately the value of this
field times the stripe width defined for the Storage Class. Note that this field only affects tape write
operations. Read operations are not limited by the value defined by this parameter.
3.10.1.9. Average Number of Storage Segments (disk only)
This parameter, along with Minimum Storage Segment Size and Maximum Storage Segment Size, is
used by the Core Server to optimally choose a storage segment size for bitfiles on disk. The Core
Server attempts to choose a storage segment size between Storage Segment Size and Maximum
Storage Segment Size that would result in creating the number of segments indicated by this field.
Guideline: For best results, it is recommended that small values (< 10) be used. This results in
minimizing metadata and optimizing migration performance. The default of 4 will be appropriate in
most situations.
3.10.1.10. PV Estimated Size / PV Size Selection
Guideline: For tape, select a value that represents how much space can be expected to be written to a
physical volume in this Storage Class with hardware data compression factored in.
Explanation: The Core Server uses this value as a guide in selecting tapes for writing, but regards it
as an estimate only. Regardless of its value, the tape will be filled before another tape is chosen for
writing.
Rule 1: For disk, the PV Size value must be the exact number of bytes available to be written on the
PV. This value must be a multiple of the media block size and the VV block size. It may be necessary
to round the actual size of the volume down to one of these multiples. The SSM will enforce these
rules when the window fields are filled in.
Rule 2: For disk, the PV Size value must be less than or equal to the Bytes on Device value described
in Section 7.1: Configure a New Device and Drive of the HPSS Management Guide.
3.10.1.11. Optimum Access Size Selection
Guideline: Generally, a good value for Optimum Access Size is the Stripe Length, which is the
Virtual Volume Block Size times the Stripe Width.
Explanation: This field is advisory in nature in the current HPSS release. In the future, it may be used
to determine buffer sizes. Generally, a good value for this field is the Stripe Length; however, in
certain cases, it may be better to use a buffer that is an integer multiple of the Stripe Length. The
simplest thing at the present time is to set this field to the Stripe Length. It can be changed in the
future without complication.
3.10.1.12. Some Recommended Parameter Values for Supported
Storage Media
Table 5 and Table 6 contain suggested values for storage resource attributes based on the media type.
The given values are not the only acceptable values, but represent reasonable settings for the various
media types. See Section 3.9.6: Location Policy on page 99 for more information about setting the
storage characteristics.
HPSS Installation Guide July 2008
Release 6.2 (Revision 2.0) 106