Computer Drive User Manual

is On Open. For all subsequently created COSes, the default value is the same as the most recent COS
configured.
Advice – Changing the Stage Code should be done with care. See Section 6.3.3: Changing a Class of
Service Definition on page 178 for detailed information on each of the choices for Stage Code.
Minimum File Size. The size, in bytes, of the smallest bitfile supported by this COS. Valid values are
any positive 64-bit integer value.
Maximum File Size. The size, in bytes, of the largest bitfile supported by this COS. Valid values are any
positive 64-bit integer value.
Allocation Method. How disk storage segments will be allocated in the storage class at the top level of
the hierarchy used by this COS. Ignored if the top level storage class is tape. Three allocation methods
are available:
● Fixed Length, Classic Style. All storage segments allocated for a single file, except possibly the
last segment of the file, are the same size. This size is computed at file creation time to be the
size which wastes the least disk space, based on the file size, the minimum and maximum
segment sizes configured for the storage class, and the average number of segments per file
configured for the storage class. In order to take maximum advantage of this allocation method,
the application creating the file must specify the file size in its file creation hints.
The application can force this fixed segment size to be the maximum segment size configured for
the storage class by specifying HINTS_FORCE_MAX_SSEG in the file creation hints.
If the application does not force the segment size to be the max size and it does not provide hints
telling the core server the file size, then the core server will use the minimum segment size
configured for the storage class.
If the file is purged completely from the top level and later restaged to the top level, a new
segment size will be computed at stage time based on the current file size.
● Fixed Length, Max Style. The size of each storage segment allocated for a file, except possibly
the last segment, is the maximum segment size configured for the storage class.
● Variable Length. The size of the first storage segment allocated for a file is the minimum
segment size configured for the storage class. The size of each successive storage segment is
twice that of the preceding segment, up to the maximum segment size configured for the storage
class. Once the max segment size is reached, each remaining segment except possibly the last is
also the max segment size.
Under all three allocation methods, the last segment of the file may be truncated to a size to best fit the
actual data contained in the segment. See the Truncate Final Segment option in the Class Flags
section below.
Class Flags
• Enforce Maximum File Size. When set, a bitfile larger than the Maximum File Size cannot be
created in this COS.
• Force Selection. A flag to determine how a COS will be selected. If ON, a client must explicitly
select this COS in order to have a file assigned to it; if the client merely supplies general COS hints
for a file, this COS will not be selected.
HPSS Management Guide November 2009
Release 7.3 (Revision 1.0) 176