Chapter 2. Software Overview
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## Chapter 2. Software Overview

The Data Migration Facility (DMF) is a comprehensive data management tool that can be used to manage free space on your native XFS or CXFS file system. DMF can also be used to manage reliable, long-term storage of important data.

DMF accomplishes its work by moving user file data between primary storage and secondary storage. This process is called file migration. File migration can occur transparently to the end user (automatic migration), or it can be invoked manually by command request ( manual migration). For a complete description of the capabilities of DMF, its commands, and the role of the IRIX or Linux system administrator, please refer to the DMF Administrator's Guide.

The following sections describe data storage and management capabilities provided with DMF, as well as the product's interface with the IRIX or Linux kernel.

## Data Storage and Management

DMF is delivered with a complete set of utilities that can be used to manage the DMF databases and control automatic space management.

The DMF components that manage offline data storage are called media-specific processes (or MSPs ) and library servers (or LSs).

| Note: Linux does not support tape MSPs. Under Linux, the LS is the only choice to manage offline tape data storage.

The LS is a newer component than the MSP and can be used instead of one or more tape MSPs, providing improved error avoidance/recovery and tape volume scratch pools. The `dmmsptols` script converts an existing tape MSP database to an LS database. It also makes any necessary changes to the daemon database. A number of DMF commands have options to facilitate the handling of library servers.

DMF is delivered with the following MSP/LS functionality:

- A tape MSP or LS that allows the administrator to designate a pool of tapes for use as a repository for stored data.

- An FTP MSP that allows the administrator to move migrated data to or from any destination machine accessible via the file transfer protocol (FTP).

- A disk MSP that migrates data into a directory accessed on the current system.

For the tape MSP/LS to manage stored data, it must mount and dismount tapes on tape transports connected to the platform on which DMF is running. Most often, tape mounting is accomplished by a robotic autoloader. These robotic autoloaders can be managed by OpenVault or by the Tape Management Facility (TMF). DMF supports all of the robotic autoloaders the mounting service supports. For a list of supported devices and libraries, refer to the `Readme` file by clicking on the Dependencies button on the DMF maintenance interface, (`dmmaint(8)`).

For a detailed description of the MSP and LS components, refer to the DMF Administrator's Guide.

Several DMF utilities are designed to ensure the integrity of DMF databases and of the media used by the tape MSP or LS. For example, you can use `dmatsnf` and `dmatread` to scan tape media looking for hard errors and to recover data from failed media. Additionally, you can examine the integrity of DMF databases by using `dmdbcheck (8)` to validate the internal structure of any DMF databaseand `dmaudit(8)` to ensure that the DMF database is consistent with the XFS/CXFS file systems being managed by DMF. For a detailed description of the use of `dmaudit`, refer to the DMF Recovery and Troubleshooting Guide.

You can automate the running of the `dmdbcheck (8)` and `dmaudit(8)` commands through the DMF configuration file, as described in DMF Administrator's Guide.

## Data Management Application Interface (DMAPI)

DMF interacts with the IRIX or Linux kernel to migrate user data. This interaction is accomplished through an interface called the Data Management Application Programming Interface or DMAPI. This interface is recognized by the X/Open Group, which calls it the XDSM standard. DMF is also supported in minor ways by the Network File System (NFS) and Bulk Data Services (BDS). You must install the DMAPI software component on any machine that will be a DMF server. It also might be necessary to install specific patches. To obtain information about specific patches, use the Dependencies button on the DMF installation interface, (`dmmaint (8)`).

## Distributed Commands

The distributed command (DC) feature is an installation subset of the full DMF product that you can install on hosts that have DMF-managed filesystems exported to them, but never execute as the DMF server host. The DC feature allows DMF user commands (`dmput`, `dmget`, `dmfind`, `dmls`, `dmcopy`, and `dmattr`) to be executed on the client host.

The DMF User Library, `libdmfusr.so`, allows users to write their own custom DMF user commands that use the same DC Application Program Interface (API) as the DMF user commands listed previously.

Licensing is installed and enforced on the DMF server machine only. No licensing is required on the client host.

## Differences from UNICOS/UNICOS/mk DMF

If you are upgrading from a UNICOS or UNICOS/mk operating system to an IRIX or Linux operating system, you will need to be aware of the differences between IRIX/Linux DMF functionality and UNICOS/UNICOS/mk DMF functionality. The basic structure of DMF is the same for IRIX or Linux environments as for UNICOS and UNICOS/mk environments. However, the differences occur in areas affected by operating system dependencies. The DMF administrator interface differs in the areas of product installation, database administration utilities, and automatic space management. There are also differences in basic terminology. Table 2-1 provides a summary of key differences between the two operating systems as they relate to DMF.

Table 2-1. IRIX/Linux and UNICOS/UNICOS/mk DMF Differences

Functionality | UNICOS/UNICOS/mk | IRIX/Linux
--- | --- | ---
Kernel interface that supports file state transitions | `dmofrq`(2) command. | DMAPI 2.3 (see “Data Management Application Interface (DMAPI)”).
Use of `HOME_DIR`, `SPOOL_DIR`, `JOURNAL_DIR` directories | No separate daemon subdirectory (daemon files in root of `HOME`, `SPOOL`, or `JOURNAL` directory). | Separate daemon subdirectory
Protected files feature | Supported as a part of the user database feature (UDB). | Not supported.
`dmmode`(2) command | Supported. | Not supported. Offline files are always processed when accessed.
Client/server configuration option | Supported. | Not supported.
Reporting | `dmhit`(blank) command. | `dmscanfs`(8) command.
DMF database administration | `dmdalter` and `dndbase` commands. | `dmdadm`(8) command, which has an administrator interface similar to that of the `dmcatadm` (8) and `dmvoladm`(8) commands.
File migration and conversion to dual state | `dmmigall`(8) command. | `dmmigrate`(8) command.
Information reporting on DMF managed files | `ls`(1) and `find`(1) commands | `dmls`(1) and `dmfind`(1) commands (based on the IRIX commands, `ls` and `find`).
Structure of directory written by the `dmsnap`(8) command | Daemon database in `snap` directory, MSP databases in `snap` directory subdirectories named for mspname | Separate daemon and MSP/LS subdirectories in `snap` directory
File handle terminology | File handle. | Bit-file identifier (`bfid` ).
File handle terminology. | `dev/inode`. | `fhandle`.

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