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Emulation of 1/2" Tape Format for 1/4" Streaming Tape Drives

IP.com Disclosure Number: IPCOM000034748D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 6 page(s) / 128K

Publishing Venue

IBM

Related People

Bakke, BE: AUTHOR [+2]

Abstract

A 1/4" streaming tape drive appears to computer system software to be a 1/2" tape drive by the user of emulation. Functions performed by this emulation include: * Map 1/2" tape Storage I/O Architecture (SIOA) commands into 1/4" tape QIC-II commands. * Map the 1/2" tape file structure into the 1/4" tape file structure. * Map the 1/2" tape label format into the 1/4" tape label format. The following terminology will be used herein: Sector - A 1/4" tape physical block whose length is equal to 512 bytes. VOL - Volume label block (Image Omitted) HDR - System Header label block HDRn - Individual System Header labels UHLn - Individual User Header labels FM - File Mark. A physical file mark that is written on tape.

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Emulation of 1/2" Tape Format for 1/4" Streaming Tape Drives

A 1/4" streaming tape drive appears to computer system software to be a 1/2" tape drive by the user of emulation. Functions performed by this emulation include: * Map 1/2" tape Storage I/O Architecture (SIOA) commands into

1/4" tape QIC-II commands.

* Map the 1/2" tape file structure into the 1/4" tape file

structure.

* Map the 1/2" tape label format into the 1/4" tape label format.

The following terminology will be used herein:

Sector - A 1/4" tape physical block whose length is equal to 512

bytes.

VOL - Volume label block

(Image Omitted)

HDR -

System Header label block

HDRn - Individual System Header labels

UHLn - Individual User Header labels

FM - File Mark. A physical file mark that is written on tape.

This is used as a delimiter between logical blocks.

BDR - Block Descriptor label block.

(Image Omitted)

DATA - User Data TRL - Trailer Label block. This could be either the End of File

(EOF) label block or the End of Volume (EOV) label block.

TRLn - Individual System Trailer labels. These could be either

the End of File (EOF) label block or the End of File (EOFn) labels

or the End of Volume (EOVn) labels.

UTLn - Individual User Trailer labels.

(Image Omitted)

LEOT - Logical End of Tape. The current end of recorded data on

the tape media. Recorded tapes generally have 3 types of logical areas (refer to

Fig. 1): 1. Volume label block

2. Files 3. Logical End of Tape indicator The volume label block is used to uniquely identify an individual piece of media (reel/cartridge) as a particular logical volume to the system. The files contain the user data and certain information (labels) that describe the file. The logical end of tape indicator marks the current end of recording on the media. The SIOA interface is a generic interface, and does not provide any distinction between the

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various types (volume labels, header labels, data, and trailer labels) of data blocks. For example, a write command issued on the SIOA interface could be a volume label write, a header label write, a data block write, or a trailer label write. The IOP determines the type (format) of the data it is processing based on the current tape position and the content of the data being read/ written. Volume Label Block: Emulation procedure (refer to Fig. 2). Write Block

1. Tape is currently positioned at beginning of tape

2. System issues a Write Block command with a data length of 80

bytes

3. Emulation:

a. Interprets command as a volume label write

b. Pads out the 80 bytes to a 512 byte 1/4" tape sector

c. Issues a QIC-II Write Data command and passes 512 byte

label sector to the 1/4" tape drive.

d. Issues a QIC-II Write File Mark on the Fly command

e. Returns operation complete

Read Block

1. Tape is currently positioned at beginning of tape

2. System issues a Read Block command with a data length of 80

bytes

3. Emulation:

a. Interprets command as a volume label read

b. Issues a QIC-II Read Data...