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Advice - Do not configure a migration policy for a storage class at the lowest level in a hierarchy.
If a migration policy is added to a storage class after files are created in the storage class, those files
may never be migrated. Use the mkmprec utility to correct this problem. See the mkmprec man page for
more information.
Purge Policy. The purge policy associated with this storage class, or None if no purge is desired.
Advice - Do not configure a purge policy for a tape storage class or for any storage class which does not
have a migration policy in effect. Purge policies only apply to disk storage classes. Purging from tape is
managed as a special characteristic of the tape migration policy.
Warning Threshold. A threshold for space used in this storage class expressed as a percentage of the
total space defined in the storage class. Alarms will be sent to SSM periodically when free space in the
storage class falls below this value, and the Space Thresholds field on the HPSS Health and Status
window will be changed to Warning. Note that this field will not have any effect if overridden by Storage
Subsystem-Specific Thresholds.
Critical Threshold. Another threshold for space used in this storage class expressed as a percentage of
the total space defined in the storage class. Alarms will be sent to SSM periodically when free space in
the storage class falls below this value, and the Space Thresholds field on the HPSS Health and Status
window will be changed to Critical. Note that this field will not have any effect if overridden by Storage
Subsystem-Specific Thresholds.
Advice - These values determine limits beyond which the MPS sends alarms indicating that storage
space is running low. The thresholds on disk are measured in bytes and expressed in terms of the
percentage of total space in the storage class. The threshold may be disabled by setting the value to 100
percent.
Optimum Access Size. The optimal transmission size to be used for a transfer request using this storage
class. (Not currently used by HPSS. May be used by site specific applications)
Average Number of Storage Segments. The Average Number of Storage Segments is used by the
Core Server as an aid in picking the size of disk storage segments when writing a file to disk. This field
is ignored when the storage class is at the top level of the hierarchy in a COS which uses Variable Length
or Fixed Length Max Style segment allocation. See the discussion of the COS Allocation Method field
and Truncate Final Segment flag in Section 6.3.2 Class of Service Configuration Window on page 175
for details on segment allocation methods.
When the storage class is at the top level of a COS which uses Fixed Length Classic Style segment
allocation, or when the storage class is at any level below the top, regardless of the COS segment
allocation method, the Core Server requires that all of the disk storage segments occupied by a given file
be the same size, and must be within the range of sizes given by the Minimum Storage Segment Size and
Maximum Storage Segment Size parameters.
If Max Storage Segment Size (MAXSEG) is greater than Min Storage Segment Size (MINSEG), the
Core Server attempts to select a storage segment size for a file such that the file can be stored in Average
Number of Storage Segments segments. If the Max Storage Segment Size (MAXSEG) is equal to the
Min Storage Segment Size (MINSEG), the Core Server will use this value for the storage segment size,
and the file will occupy as many of these segments as necessary.
The principal effect of changing the value of the Average Number of Storage Segments is on disk
volume fragmentation. If the files to be stored in a storage class are large relative to the size of the disk
HPSS Management Guide November 2009
Release 7.3 (Revision 1.0) 160