Hub/Switch Installation Guide

Chapter 2 HPSS Planning
HPSS Installation Guide September 2002 105
Release 4.5, Revision 2
2.9.3.6 Selecting Transfer Rate
This field can be used via the COS Hints mechanism to affect COS selection.
Guideline 1: This field should generally be set to the value of the Transfer Rate field in the storage
class that is at the top level in the hierarchy. This should always be the case if the data is being
staged on open.
Guideline 2: If a large percentage of the reads are being done from a lower level in the hierarchy,
considersettingthetransferrate basedontheTransferRate associatedwiththe storageclassatthis
lower level.
2.9.3.7 StripeLength and StripeWidth Hints
These fields can be used via the COS Hints mechanism to affect COS selection.
Guideline: StripeLength and StripeWidth hints are available in the hints mechanism. When
specified in the hints, StripeLength and StripeWidth from the storage class at the top level of each
hierarchy are used in the COS selection algorithm.
2.9.4 File Families
Each file in HPSS is assigned a family designation. A family can be assigned to a fileset, then any
file created in that fileset will belong to that family. The default family is family zero, which is
interpreted by the system as meaning that the file is not associated with a family. The family
designation has no effect on the placement of files on disk, but does control the tape to which the
file migrates. HPSS will select a tape that has been assigned to the file’s family when the file is
migratedto tape.If notapeshavebeenassigned tothe family, orall tapesassignedtothefamily are
busy, andif othertape assignment criteriaaremet (e.g. maxactivetapesper storageclass), thetape
storage server will assign a blank tape to the family and the file will migrate to it.
HPSSplaces norestrictiononthevalues assignedtothe FileFamily IDs,otherthanzerois reserved
by the system toindicate thatafile has no family association. Aname mustbeassigned to each file
family.
Defining multiple file families may have an impact on system migration performance. MPS may
have to mount a significantly larger number of tapes to complete a migration from a disk storage
classifthe filesarespreadacrossalargenumberoffile families,comparedtothenumberofmounts
that would be required if all the files were in the same family.
2.10 HPSS Sizing Considerations
This section will help define the amount of storage that is needed for various aspects of HPSS,
including storage for user files, user directories, and the additional metadata storage needed for
servers to control various operations on files.