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-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
-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
-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.
--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.
-- Performance sometimes is rather low because we don't fully exploit clustering
-- 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)