Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 DASD device driver 2 3 S/390's disk devices (DASDs) are managed by Linux via the DASD device 4 driver. It is valid for all types of DASDs and represents them to 5 Linux as block devices, namely "dd". Currently the DASD driver uses a 6 single major number (254) and 4 minor numbers per volume (1 for the 7 physical volume and 3 for partitions). With respect to partitions see 8 below. Thus you may have up to 64 DASD devices in your system. 9 10 The kernel parameter 'dasd=from-to,...' may be issued arbitrary times 11 in the kernel's parameter line or not at all. The 'from' and 'to' 12 parameters are to be given in hexadecimal notation without a leading 13 0x. 14 If you supply kernel parameters the different instances are processed 15 in order of appearance and a minor number is reserved for any device 16 covered by the supplied range up to 64 volumes. Additional DASDs are 17 ignored. If you do not supply the 'dasd=' kernel parameter at all, the 18 DASD driver registers all supported DASDs of your system to a minor 19 number in ascending order of the subchannel number. 20 21 The driver currently supports ECKD-devices and there are stubs for 22 support of the FBA and CKD architectures. For the FBA architecture 23 only some smart data structures are missing to make the support 24 complete. 25 We performed our testing on 3380 and 3390 type disks of different 26 sizes, under VM and on the bare hardware (LPAR), using internal disks 27 of the multiprise as well as a RAMAC virtual array. Disks exported by 28 an Enterprise Storage Server (Seascape) should work fine as well. 29 30 We currently implement one partition per volume, which is the whole 31 volume, skipping the first blocks up to the volume label. These are 32 reserved for IPL records and IBM's volume label to assure 33 accessibility of the DASD from other OSs. In a later stage we will 34 provide support of partitions, maybe VTOC oriented or using a kind of 35 partition table in the label record. 36 37 USAGE 38 39 -Low-level format (?CKD only) 40 For using an ECKD-DASD as a Linux harddisk you have to low-level 41 format the tracks by issuing the BLKDASDFORMAT-ioctl on that 42 device. This will erase any data on that volume including IBM volume 43 labels, VTOCs etc. The ioctl may take a 'struct format_data *' or 44 'NULL' as an argument. 45 typedef struct { 46 int start_unit; 47 int stop_unit; 48 int blksize; 49 } format_data_t; 50 When a NULL argument is passed to the BLKDASDFORMAT ioctl the whole 51 disk is formatted to a blocksize of 1024 bytes. Otherwise start_unit 52 and stop_unit are the first and last track to be formatted. If 53 stop_unit is -1 it implies that the DASD is formatted from start_unit 54 up to the last track. blksize can be any power of two between 512 and 55 4096. We recommend no blksize lower than 1024 because the ext2fs uses 56 1kB blocks anyway and you gain approx. 50% of capacity increasing your 57 blksize from 512 byte to 1kB. 58 59 -Make a filesystem 60 Then you can mk??fs the filesystem of your choice on that volume or 61 partition. For reasons of sanity you should build your filesystem on 62 the partition /dev/dd?1 instead of the whole volume. You only lose 3kB 63 but may be sure that you can reuse your data after introduction of a 64 real partition table. 65 66 BUGS: 67 - Performance sometimes is rather low because we don't fully exploit clustering 68 69 TODO-List: 70 - Add IBM'S Disk layout to genhd 71 - Enhance driver to use more than one major number 72 - Enable usage as a module 73 - Support Cache fast write and DASD fast write (ECKD)