| DASD device driver | |
| S/390's disk devices (DASDs) are managed by Linux via the DASD device | |
| driver. It is valid for all types of DASDs and represents them to | |
| Linux as block devices, namely "dd". Currently the DASD driver uses a | |
| single major number (254) and 4 minor numbers per volume (1 for the | |
| physical volume and 3 for partitions). With respect to partitions see | |
| below. Thus you may have up to 64 DASD devices in your system. | |
| The kernel parameter 'dasd=from-to,...' may be issued arbitrary times | |
| in the kernel's parameter line or not at all. The 'from' and 'to' | |
| parameters are to be given in hexadecimal notation without a leading | |
| 0x. | |
| If you supply kernel parameters the different instances are processed | |
| in order of appearance and a minor number is reserved for any device | |
| covered by the supplied range up to 64 volumes. Additional DASDs are | |
| ignored. If you do not supply the 'dasd=' kernel parameter at all, the | |
| DASD driver registers all supported DASDs of your system to a minor | |
| number in ascending order of the subchannel number. | |
| The driver currently supports ECKD-devices and there are stubs for | |
| support of the FBA and CKD architectures. For the FBA architecture | |
| only some smart data structures are missing to make the support | |
| complete. | |
| We performed our testing on 3380 and 3390 type disks of different | |
| sizes, under VM and on the bare hardware (LPAR), using internal disks | |
| of the multiprise as well as a RAMAC virtual array. Disks exported by | |
| an Enterprise Storage Server (Seascape) should work fine as well. | |
| We currently implement one partition per volume, which is the whole | |
| volume, skipping the first blocks up to the volume label. These are | |
| reserved for IPL records and IBM's volume label to assure | |
| accessibility of the DASD from other OSs. In a later stage we will | |
| provide support of partitions, maybe VTOC oriented or using a kind of | |
| partition table in the label record. | |
| USAGE | |
| -Low-level format (?CKD only) | |
| For using an ECKD-DASD as a Linux harddisk you have to low-level | |
| format the tracks by issuing the BLKDASDFORMAT-ioctl on that | |
| device. This will erase any data on that volume including IBM volume | |
| labels, VTOCs etc. The ioctl may take a 'struct format_data *' or | |
| 'NULL' as an argument. | |
| typedef struct { | |
| int start_unit; | |
| int stop_unit; | |
| int blksize; | |
| } format_data_t; | |
| When a NULL argument is passed to the BLKDASDFORMAT ioctl the whole | |
| disk is formatted to a blocksize of 1024 bytes. Otherwise start_unit | |
| and stop_unit are the first and last track to be formatted. If | |
| stop_unit is -1 it implies that the DASD is formatted from start_unit | |
| up to the last track. blksize can be any power of two between 512 and | |
| 4096. We recommend no blksize lower than 1024 because the ext2fs uses | |
| 1kB blocks anyway and you gain approx. 50% of capacity increasing your | |
| blksize from 512 byte to 1kB. | |
| -Make a filesystem | |
| Then you can mk??fs the filesystem of your choice on that volume or | |
| partition. For reasons of sanity you should build your filesystem on | |
| the partition /dev/dd?1 instead of the whole volume. You only lose 3kB | |
| but may be sure that you can reuse your data after introduction of a | |
| real partition table. | |
| BUGS: | |
| - Performance sometimes is rather low because we don't fully exploit clustering | |
| TODO-List: | |
| - Add IBM'S Disk layout to genhd | |
| - Enhance driver to use more than one major number | |
| - Enable usage as a module | |
| - Support Cache fast write and DASD fast write (ECKD) |