HPSS Servers
|
WARNING: SciNet is in the process of replacing this wiki with a new documentation site. For current information, please go to https://docs.scinet.utoronto.ca |
HPSS servers include the Core Server, Migration/Purge Server, Gatekeeper, Location Server, Log Client, Log Daemon, Physical Volume Library, Physical Volume Repository, Mover, Storage System Management System Manager, and Startup Daemon. Figure 3: HPSS Components provides a simplified view of the HPSS system. Each major server component is shown, along with the basic control communication paths (thin arrowed lines). Infrastructure items (those components that “glue together” the distributed servers) are shown at the top of the cube.
Core Server. The Core Server provides several key sets of functionality.
First, the Core Server provides translation between human-oriented names and HPSS object identifiers. Name space objects managed by the Core Server are filesets, junctions, directories, files, hard links, and symbolic links. The Core Server provides access verification to objects and mechanisms for manipulating access to these objects via a Portable Operating System Interface (POSIX) view of the name space. This name space is a hierarchical structure consisting of directories, files, and links. These name space objects may exist within filesets that are connected via junctions.
Second, the Core Server provides the abstraction of logical bitfiles to its clients. A bitfile is identified by a Core Server generated name called a bitfile ID. Clients may reference portions of a bitfile by specifying the bitfile ID and a starting address and length. The Core Server supports random access to files and sparsely written files. It supports parallel reading and writing of data to bitfiles and performs the mapping of logical portions of bitfiles onto physical storage devices. The Core Server supports the migration, purging, and staging of data in a storage hierarchy (though the migration/purge policies are implemented through the Migration/Purge Server, a client to the Core Server).
Third, the Core Server provides a hierarchy of storage objects: storage segments, virtual volumes, and physical volumes. The Core Server translates storage segment references into virtual volume references and then into physical volume references, handles the mapping of physical resources into striped virtual volumes to allow parallel I/O to that set of resources, and schedules the mounting and dismounting of removable media through the Physical Volume Library (see below).
Migration/Purge Server (MPS). The MPS allows a site to implement its storage management policies by managing the placement of data on HPSS storage media using site-defined migration and purge policies. By making appropriate calls to its Core Server, an MPS copies data to lower levels in the hierarchy (migration), removes data from the current level once copies have been made (purge), or moves data between volumes at the same level (lateral move). Based on the hierarchy configuration, MPS can be directed to create duplicate copies of data when it is being migrated from disk or tape. This is done by copying the data to multiple lower levels in the storage hierarchy.
There are three types of migration: disk migration, tape file migration, and tape volume migration. The designation disk or tape refers to the type of storage class that migration is running against. See Section 3.7.2: Migration/Purge Server on page 72 for a more complete discussion of the different types of migration.
MPS runs migration on each storage class periodically using the time interval specified in the migration policy for that class. See Section 2.3.7: HPSS Policy Modules on page 34 for details on migration and purge policies. Migration runs can be started automatically when the warning or critical space thresholds for the storage class are exceeded. In addition, migration runs can be started manually by an administrator.
Purge runs are started automatically on each storage class when the free space in that class falls below the percentage specified in the purge policy. Purge runs may also be started manually.
Disk Migration/Purge: The purpose of disk migration is to make one or more copies of disk files to lower levels in the hierarchy. The number of copies depends on the configuration of the hierarchy. For disk, migration and purge are separate operations. It is common for disk storage classes which have been configured for migration to also be configured for purge as well. Once a file has been migrated (copied) downwards in the hierarchy, it becomes eligible for purge, which subsequently removes the file from the higher level and allows the disk space to be reused.
Tape File Migration: The purpose of tape file migration is to make an additional copy (or multiple additional copies) of a file, in a tape storage class, to a lower level in the hierarchy. It is also possible to move files downwards instead of copying them. In this case there is no duplicate copy maintained. There is no separate purge component to tape file migration. Empty volumes must be reclaimed using the reclaim utility.
Tape Volume Migration: The purpose of tape volume migration is to free tape volumes for reuse. Tape volumes are selected based on being in the EOM map state and containing the most unused space (caused by users overwriting or deleting files). The remaining segments on these volumes are either migrated downwards to the next level in the hierarchy, or are moved laterally to another tape volume at the same level. This results in empty tape volumes which may then be reclaimed. Note that there is no purge component to tape volume migration. All of the operations use a move instead of a copy semantic.
Gatekeeper (GK). The Gatekeeper provides two main services:
- It provides sites with the ability to schedule the use of HPSS resources using the Gatekeeping Service.
- It provides sites with the ability to validate user accounts using the Account Validation Service.
Both of these services allow sites to implement their own policy.
The default Gatekeeping Service policy is to not do any gatekeeping. Sites may choose to implement a policy for monitoring authorized callers, creates, opens, and stages. The Core Server will call the appropriate GK API depending on the requests that the site-implemented policy is monitoring.
The Account Validation Service performs authorizations of user storage charges. A site may perform no authorization, default authorization, or site-customized authorization depending on how the Accounting Policy is set up and whether or not a site has written site-specific account validation code. Clients call this service when creating files, changing file ownership, or changing accounting information. If Account Validation is enabled, the Account Validation Service determines if the user is allowed to use a specific account or gives the user an account to use, if needed. The Core Server also calls this service to perform an authorization check just before account-sensitive operations take place.
Location Server (LS). The Location Server acts as an information clearinghouse to its clients through the HPSS Client API to enable them to locate servers and gather information from both local and remote HPSS systems. Its primary function is to allow a client to determine a server's location and, by knowing other information about the server such as its object UUID, determine its server type or its subsystem id. This allows a client to contact the appropriate server. Usually the Location Server is only used by the Core Server or the Gatekeeper.
Physical Volume Library (PVL). The PVL manages all HPSS physical volumes. It is in charge of mounting and dismounting sets of physical volumes, allocating drive and cartridge resources to satisfy mount and dismount requests, providing a mapping of physical volume to cartridge and of cartridge to Physical Volume Repository (PVR), and issuing commands to PVRs to perform physical mount and dismount actions. A primary function of the PVL is the support for atomic mounts of sets of cartridges for parallel access to data. Atomic mounts are implemented by the PVL, which waits until all necessary cartridge resources for a request are available before issuing mount commands to the PVRs.
Physical Volume Repository (PVR). PVRs manage HPSS cartridges. Though an HPSS system may contain multiple PVRs, each cartridge is managed by only one. PVRs provide APIs for clients to request cartridge mounts and dismounts and query the status of cartridges. For convenience, PVRs are often configured in one-to-one correspondence to tape libraries.
For information on the types of tape libraries supported by HPSS PVRs, see Section 3.4.2:Robotically Mounted Tape on page 49.
An Operator PVR is provided for cartridges not under control of a robotic library. These cartridges are mounted on a set of drives by operators.
- Mover (MVR). The purpose of the Mover is to transfer data from a source device to a sink device. A device can be a standard I/O device with geometry (e.g., tape, disk) or a device without geometry (e.g., network, memory). The Mover’s client (typically the Core Server) describes the data to be moved and where the data is to be sent. It is the Mover’s responsibility to actually transfer the data, retrying failed requests and attempting to optimize transfers. The Mover supports transfers for disk devices, tape devices and a mover protocol that can be used as a lightweight coordination and flow control mechanism for large transfers.
- Log Client (LOGC). The Log Client receives log messages from each HPSS server running on its node and filters those messages based on the configured log policies. Log messages which pass the filter are written to a local log and sent on to the Log Daemon.
- Log Daemon (LOGD). The Log Daemon enters log messages into the central log file and sends those messages which are to be displayed in the Alarms and Events SSM window to the SSM System Manager.
Storage System Management System Manager (SSMSM). SSM, the Storage System Management subsystem, is the tool used by the system administrator to manage HPSS. SSM has three components, one of which is an HPSS server and two of which are user interface client programs. The server is:
- SSM System Manager (SSMSM, or hpss_ssmsm) - Communicates with all other HPSS components requiring monitoring or control.
The user interface clients are:
- SSM GUI (hpssgui) - Provides the HPSS administrator or operator the ability to configure or monitor the HPSS System through a graphical user interface.
- SSM Command Line Interface (hpssadm) - Provides the HPSS administrator or operator the ability to configure or monitor a subset of the HPSS system through a set of interactive or batch commands.
- SSM enables the administrator to configure, monitor and control the resources (servers, devices, tape libraries, and media) of HPSS in ways that conform to the management policies of a given customer site.
Monitoring capabilities include the ability to query the values of important management attributes of storage system resources and the ability to receive notifications of alarms and other significant system events. Controlling capabilities include the ability to start up and shut down servers and the ability to set the values of management attributes of storage system resources and storage system policy parameters. Additionally, SSM can request that specific operations be performed on resources within the storage system, such as adding and deleting logical or physical resources.
Startup Daemon. The Startup Daemon is called by the SSMSM to start each HPSS server except the SSMSM, the Startup Daemon itself, and the remote portion of the Mover. A Startup Daemon is required on each node where any HPSS Server executes, with the exception that no Startup Daemon is required on nodes where the only HPSS Server is the remote portion of the Mover.