Device classes are TSM storage objects that contain information about the device type and the media.
TSM supports many devices for storing data. Devices known to TSM may be devices that exist as real physical devices, such as a disk drive or a tape drive. Devices may also be logical devices, such as files on a disk (FILE device type) or storage on another server (SERVER device type).
At a minimum, each type of device requires a device class. The device class contains information for the management of devices and media that are of a specific device type. The device type determines whether TSM also requires a library and drive definition. For example, a manually mounted tape device requires a device class, a library, and a drive definition.
Disk devices access their media randomly and share a single, common TSM device class named DISK. Administrators cannot define other random access device classes. Do not define a TSM library for random access devices.
Magnetic disk devices are the only devices in the random access category. All disk devices share the same TSM device type and device class: DISK. TSM has a predefined DISK device class.
Figure 121. Magnetic Disk Devices Are Represented by Only a Device Class
Tape devices, other devices that use removable media, FILE device types, and SERVER device types are members of the sequential access category of devices. All of these devices access their data sequentially. A device class for a sequential device contains a device type and media management information.
For sequential devices, the device class also specifies a library. Figure 122 shows the contents of a device class for a typical sequential access device.
Figure 122. Contents of a Device Class for Sequential Access Devices
Sequential access device types begin to store data at the beginning of a volume, and append new data after existing data. As data is deleted or expired, the space is not immediately reused. The server can reclaim space later by using the reclamation process (see Reclaiming Space in Sequential Access Storage Pools for details).
Every sequential access device class requires a TSM device type as part of its definition. A device type identifies a device as a member of a group of devices that share similar media characteristics, for example an 8MM device type for tape drives that use 8mm tape. Device types supported by TSM include the following:
Administrators can use FILE volumes as a way to use disk storage without having to define volumes to TSM. FILE volumes can also be useful when transferring data for purposes such as electronic vaulting.
Virtual volumes can be used for:
Figure 123. Removable Media Devices Are Represented by a Library, Drive, and Device Class
For sequential access device types (excluding FILE and SERVER), administrators must specify a library in the device class definition. The library administrators specify must be one that was defined to TSM, as discussed in Libraries.
Every sequential access device class contains media management information, such as recording format and labeling prefixes.
For more information about how TSM helps to manage media, see Chapter 6, Managing Removable Media Operations.