Chapter 7 HPSS User Interface Configuration440 September 2002 HPSS Installation GuideRelease 4.5, Revision 2To support persistent DM-related metadata, XFS utilizes its standard extended attribute facility.DM attributes, event masks, managed regions, and attribute change times (dtime values) are storedas extended attributes. These extended attributes are treated as file metadata.The xfsdump and xfsrestore utilities include extended attributes and migrated regions. Migrateddata is not recalled when a dump is taken, producing an abbreviated dump.7.6.2.6 HPSS Components Required to Support DFS and XFSAn HPSS Data Management Application (HPSS/DMAP or HDM) and a DMAP Gateway must beconfigured into the HPSS system if an integrated HPSS/DFS or HPSS/XFS system is to besupported at your site.7.6.2.6.1 HPSS/DMAP (HDM) ServerHDM is responsible for initiating and coordinating name space and data interactions between themanaged file system and HPSS. It catches and processes desired name and data space eventsgenerated by the managed file system, migrates file data to HPSS, purges unneeded file data fromthe managed file system after migration, and processes requests originating in HPSS interfaces thatrequire either name or data resources from the managed file system. HDM resides on the samemachine where the managed file system is running. HDM communicates with HPSS componentsvia XDR over TCP sockets.HDM registers to receive name and data space events originating in the managed file system. Aftercatching a name space event involving a mirrored fileset, the appropriate requests are made toHPSS to keep the name spaces synchronized. However, for archived filesets, only create anddestroy name space events are processed, but no HPSS resources are utilized until the file ismigrated to HPSS. HDM receives data space events when a file is read, written, or truncated andthe data region involved is registered via XDSM. HDM is responsible for caching data to themanaged file system that is not present; invalidating HPSS data, if necessary; and manipulatingdata regions to minimize the occurrence of events involving the same region. HDM can cachepartial files with DFS but must cache whole files for XFS due to a constraint on the number ofmanaged regions supported by XFS.HDM provides an interface for HPSS to request that an action occur in DFS to keep the HPSS andDFS name and data spaces synchronized. This mechanism is only used with mirrored filesets whenan HPSS client requests to create, delete or modify a name space object. This interface is also usedby HPSS to migrate or purge data from Episode disks. Before file data can be altered through HPSSinterfaces, the data must first be purged from Episode disks. The capability to forward DCEcredentials is provided, enabling HDM to make DFS requests on behalf of the end user.HDM migrates file data from the managed file system to HPSS. It also purges file data from themanaged file system to free disk resources. For DFS, only data that has been modified on themanaged file system is migrated to HPSS, thus, a minor modification to a very large file will notresult in re-migrating the entire file. Because policies for migrating and purging data are separatelyconfigurable, file data migrated from a managed file system is not automatically purged. In manycases, data for a given file will be present in both the managed file system and HPSS and can beread from either interface without any data migration or staging.
