The Full Form of DASD is‍ Direct access storage device.

Direct access storage devices (DASDs) are fixed or removable storage devices. Typically, these devices are rotating disk drives or solid state disks. A fixed storage device is any storage device defined during system configuration to be an integral part of the system DASD. The operating system detects an error if a fixed storage device is not available at some time during normal operation.

A removable storage device is any storage device defined by the person who administers your system during system configuration to be an optional part of the system DASD. The removable storage device can be removed from the system at any time during normal operation. As long as the device is logically unmounted first, the operating system does not detect an error.

The following types of devices are not considered DASD and are not supported by the logical volume manager (LVM):

• CD-ROM (compact disk read-only memory)
• DVD
• WORM (write-once read-many)