Direct Access Storage Device

A Direct Access Storage Device (DASD ) is a device for direct memory access.

With a data storage device DASD category you can directly access information without having to work through all the memory areas sequentially until the desired element. While there is a DASD in a floppy disk drive, which is in the magnetic tape apparatus is not the case, since the data is stored as a linear blocks.

Different DASD disciplines

ECKD (Extended Count Key Data)

  • Mainly used DASD discipline
  • Different block sizes in non-Linux systems
  • Two different formats (LDL and CDL )

FBA (Fixed Block Architecture )

  • Less common
  • Fixed block size (usually 512 bytes )

DIAG (DIAG -accessed )

  • Rarely used
  • Kernel 2.4 - CMS minidisk Reserved
  • Kernel 2.6 - each VM administered Disk ( alternative method )
  • Storage drive