mc(7) —
NAME
mc − mini-cartridge tape driver for Irwin drives
DESCRIPTION
mc is the name of a mini-cartridge device driver for Irwin floppy interface tape drives. Features include:
Runs in AT and PS/2 hardware environments. Supports all production Irwin floppy interface (MFM) drives. Uses Reed-Solomon ECC. Provides read/write compatibility for AccuTrak format tapes. Offers read/write compatibility with older XENIX format tapes. Uses system floppy controller or Irwin 4100/4100MC controllers. Uses 1Mb floppy transfer rate (when hardware permits). Relocates blocks on write errors. Works with one or two drives (non-simultaneous).
When installed (see the “INTERACTIVE UNIX Operating System Maintenance Procedures”) and booted, the driver uses the daemon startup program /etc/mcdaemon to provide background ECC encode/decode. The utility program /bin/mcart provides device-specific commands such as drive model information, cartridge state information, tape retensioning and rewinding, and formatting. Users can also use the common tape control front-end program, mt, to access these functions.
Minor Numbers and Special Files
Normally, tape is used to back up and restore data.
In the normal mode of operation, the mc driver does the following in order to ensure reliable data retrieval:
1. Encodes and decodes ECC (except for 110 drives).
2. Maps out defective blocks listed in the tape header block.
3) Relocates data to a block in a spare area when a block is found to be defective during writing.
There are several possible modes for mapping tape blocks. For any given tape, the mapping mode used is dependent on the tape header information (when a header exists) stored in the first block(s), the format of the header, and whether ECC was used. There are tape drivers at various installations that use mapping modes that are different from the ones normally used by the mc driver. During a restore operation, the mapping mode that was originally used to write data is significant.
In order to accommodate tapes written by other drivers and also for diagnostic purposes, the mc driver supports several mapping modes. A particular mapping mode is selected by encoding the mode in the mc driver special file’s minor number. The minor number also encodes a logical drive number since the driver supports two tape units.
The bits of the 8-bit minor number have meanings to the mc driver as shown in the following table:
| Bit number: | 76543210 | |
| Bit name: | rMMMrrrU | |
| Where: | r: | Reserved bit − must be zero |
| MMM: | ||
| U: |
The following table gives mapping mode numbers (MMM), the convention used for naming the special file associated with the mode, and a description of the mode. In the special file name, the letter “U” is replaced with a tape drive logical unit number “0” or “1.”
| Special | ||
| Map | File | |
| Mode | Name | Description |
| 0 | rmcU | Mapped mode. This is the normal mode for tape read/write access. This mode recognizes tapes with either Irwin headers or older-style XENIX headers in physical block 0. For both header styles, defects are mapped out according to a defect list. ECC is encoded during write operations. ECC is decoded, when necessary, for read data recovery. When an Irwin header is present (i.e., AccuTrak tapes or tapes formatted with the mc, SCO UNIX, or SCO SLS drivers), the mc driver reserves the first three good blocks for header and relocation table information. The user data area starts in the fourth good tape block. A relocation table is written on the first device write for a tape which has none. When a medium error is encountered during a write operation, the block is relocated to a spare area at the end of the tape. When an older style XENIX header is present, the user data area starts in the second good tape block. No relocation table is written. |
| 1 | rmcUp | Physical block mapping. This mode is intended for diagnostic use. All data (not ECC) sectors are accessible starting with the first sector in physical block 0. Defects are not mapped out. ECC is encoded for writes, and decoded, when necessary, for read data recovery. |
| 2 | rmcUpl | Physical long block mapping. This mode is intended for diagnostic use. All data and ECC sectors are accessible starting with the first sector in physical tape block 0. Defects are not mapped out. ECC is not encoded for writes, but ECC is decoded, when necessary, for read data recovery. |
| 4 | rmcUa | All sectors have data mode. This is a compatibility mode for tape backups created with early INTERACTIVE tape drivers. Since all sectors contain data starting with the first sector of physical tape block 0, there is no defect mapping and no ECC. Writing tapes with this mapping mode is discouraged. |
| 5 | rmcUnr | Mapped mode with no relocation table. This device file is used for compatibility with the SCO SLS and SCO UNIX drivers. It is similar to map mode 0 with the exception that no relocation table is written on the first write. If, however, a relocation table is present, it is used. |
| 7 | mcdaemon | This is a special file used by the daemon process. |
The following list shows the commands used to create the special files used to access all mapping modes and drives. In this list, MAJOR represents an installation-specific major device number:
| mknod /dev/mc/rmc0 | c MAJOR 0 |
| mknod /dev/mc/rmc0p | c MAJOR 16 |
| mknod /dev/mc/rmc0pl | c MAJOR 32 |
| mknod /dev/mc/rmc0a | c MAJOR 64 |
| mknod /dev/mc/rmc0nr | c MAJOR 80 |
| mknod /dev/mc/rmc1 | c MAJOR 1 |
| mknod /dev/mc/rmc1p | c MAJOR 17 |
| mknod /dev/mc/rmc1pl | c MAJOR 33 |
| mknod /dev/mc/rmc1a | c MAJOR 65 |
| mknod /dev/mc/rmc1nr | c MAJOR 81 |
| mknod /dev/mc/mcdaemon | c MAJOR 112 |
SEE ALSO
“INTERACTIVE UNIX Operating System Maintenance Procedures” in the INTERACTIVE UNIX Operating System Guide.
ADDED VALUE
This entry, supplied by INTERACTIVE Systems Corporation, is an extension of UNIX System V.
\*U — Version 1.0