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