Managing extent space efficient DASDs

The Linux® kernel recognizes ESE DASDs. You can set them online and use them as usual, without taking any special action.

ECKD DASD devices require preformatted tracks to function as Linux block devices. Therefore, running dasdfmt on a new ECKD DASD is mandatory to make the device usable. If an unformatted track is accessed on a standard volume, the driver displays errors, such as, "The specified record was not found."

In contrast, the driver can format ESE volumes on-demand upon first access of records, eliminating the need for full device formatting before use.

Due to this design, copy-pair setups where ESE volumes are mirrored to standard volumes can become unusable for Linux. This happens when the storage server initializes unallocated tracks on the ESE volume as unformatted tracks on the standard DASD volume, causing the resulting copy to be incompatible with Linux. Similar issues can arise in specific z/VM setups if a 1-END or 0-END ESE-allocated minidisk is transferred to a non-full-pack minidisk.