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movement protocol overhead and helps to keep the data streams flowing smoothly.
VV Block Size must meet the following constraining requirements:
• It must be an integer multiple of the Media Block Size.
• The PV Section Length (Media Block Size (MBS) * Blocks Between Tape Marks (BBTM)
divided by the VV Block Size (VVBS) must be a whole number. For example, if the Media
Block Size (MBS) is 64 KB, and the Blocks Between Tape Marks (BBTM) is 512, the physical
volume section length is 32 MB. The VV Block Size (VVBS) could be 64 K, 128 K, 256 K, or
larger, but not 192 K.
See the HPSS Installation Guide , Section 3.10.1.2: Virtual Block Size Selection (disk) and Section
3.10.1.3:Virtual Block Size Selection(tape) for information.
Stripe Width (SW). The number of Physical Volumes in a Virtual Volume in this Storage Class.
PV Size (PVSIZE). The estimated size of the tape volume in bytes. The actual number of bytes that can
be written to a tape will vary with individual media and data compressibility. Think of this field as the
nominal length of a tape of this type.
VV SIZE (VVSIZE). The virtual volume size. The product of the PV Size (PVSIZE) and the Stripe
Width (SW).
Stripe Length (SL). The Stripe Length (SL) is the product of the VV Block Size (VVBS) and the
Stripe Width (SW).
Transfer Rate
Device I/O Rate (DIOR). The approximate data transfer speed, in kilobytes per second (KB/sec), which
can be achieved by devices corresponding to Media Type.
Advice - This field is used in calculating a reasonable setting for Seconds Between Tape Marks
(SBTM).
Stripe Transfer Rate (STR). The estimated aggregate transfer rate for volumes of this type. This field is
calculated using the Stripe Width (SW) times the Device I/O Rate (DIOR).
Seconds Between Tape Marks (SBTM). The number of seconds between tape mark writes while
writing continuously to tape.
Advice - The Device I/O Rate (DIOR), the Media Block Size (MBS) and the Seconds Between Tape
Marks (SBTM) determine the length of a physical volume section. The administrator should set the
Device I/O Rate (DIOR) to an appropriate value for the device, and then pick a Media Block Size
(MBS). Finally, adjust the Seconds Between Tape Marks (SBTM) to strike a balance between tape
utilization and transfer efficiency.
Smaller values of Seconds Between Tape Marks (SBTM) cause more tape to be consumed in tape marks
and break up data streaming throughput on streaming tape drives, but cause controller buffers to be
flushed more frequently and may improve access times to the middle of large files.. Larger values
improve transfer efficiency. However, smaller values may reduce the amount of data that may need to be
re-written on another tape when a tape reaches EOM. As tape drive streaming rates increase, we
generally recommend larger values for this setting.
HPSS Management Guide November 2009
Release 7.3 (Revision 1.0) 165