metadata updates and can impose extra overhead on DB2. Also, unpredictable purge behavior may be
observed if the purge record ordering is changed with existing purge records in the system until these
existing records are cleared. A purge run ends when either the supply of purge records is exhausted or
the purge target is reached.
There are two different tape migration methods, tape volume migration and tape file migration. The
method which is applied to a tape storage class is selected in the migration polic y for that storage
class. Tape volume migration's goal is freeing tape volumes by moving data segments from sparsely
filled volumes either laterally (to another tape within the same storage class) or vertically (to a lower
level in the storage hierarchy). Tape file migration can be thought of as a hybrid between the disk
and tape volume migration methods. It is a file-based tape method which is able to make a single
copy of tape files to the immediately lower level in the hierarchy. For details on tape migration
options, please see Section 3.9.1.2: Migration Policy on page 95.
If, at any point during a tape file migration run, the MPS detects that the source tape volume has
become active, migration is abandoned on this volume until the next migration run. This is done in
order to avoid competing with an HPSS system user for this volume. A tape volume is deemed to be
active if any file it contains has been read or written within the access intervals specified in the
migration policy.
The MPS provides the capability of generating migration/purge report files that document the
activities of the server. The specification of the UNIX report file name prefix in the MPS server
specific configuration enables the server to create these report files . It is suggested that a complete
path be provided as part of this file name prefix. Once reporting is enabled, a new report file is started
every 24 hours. The names of the report files are made up of the UNIX file name prefix from the
server specific configuration, plus a year-month-day suffix. With reporting enabled, MPS will
generate file-level migration and purge report entries in real time. These report files can be
interpreted and viewed using the mps_reporter utility. Since the number and size of the report files
grow rapidly, each site should develop a cron job that will periodically remove the reports that are no
longer needed.
In order to efficiently perform disk migration, the MPS parallelizes the migration of files from disk to
tape. The number of files that the MPS migrates simultaneously is user configurable via the Request
Count in the Disk Migration Policy. For example, if the Request Count is set to one, then the MPS
will serially migrate files. If the Request Count is set to four, then the MPS will attempt to have four
files migrating at a time.
As previously indicated, the MPS provides the information displayed in the HPSS Active Storage
Classes window in SSM. Each MPS contributes storage class usage information for the re sources
within its storage subsystem. MPS accomplishes this by polling the Core Server within its subs ystem
at the interval specified in the MPS server specific configuration. The resulting output is one line for
each storage class for each storage subsystem in which that class is enabled. The M PS for a
subsystem does not report on storage classes which are not enabled within that subsystem. The
warning and critical storage class thresholds are also activated by the MPS.
3.7.3. Gatekeeper
Each Gatekeeper may provide sites with the ability to:
•Schedule the use of HPSS resources using Gatekeeping Services.
•Validate user accounts using the Account Validation Service.
If the site doesn’t want either service, then it is not necessary to configure a Gat ekeeper into the
HPSS system.
HPSS Installation Guide July 2008
Release 6.2 (Revision 2.0) 84