Exabyte EXB-8505 8mm manual Long Filemarks, 2Type and size of filemarks for each format

2 Recording Format

Filemarks

Filemarks enable the initiator to locate particular blocks of data on the tape quickly during a high-speed search. By using a SPACE filemark (11h) command, the initiator can position the tape to the data marked by filemarks at up to 75 times the normal tape speed (or up to 10 times the normal tape speed when reading an 8200 format tape).

Depending on the format, the tape drive can write either a long or short filemark. Table 2-2shows the type and size of filemarks for each format type.

Table 2-2Type and size of filemarks for each format

	Type and size of filemarks
Tape format
	Long filemark	Short filemark
	(KBytes)	(KBytes)
8500 or	48	1
8500c
8200	2,160	184
8200c	2,160	1

Long Filemarks

A long filemark in either 8500 or 8500c format consists of six tracks of information:

Two gap tracks at the beginning

Two tracks of filemark physical blocks

Two gap tracks at the end

A long filemark in 8200c or 8200 format consists of the following:

An erase gap equivalent in length to 249 tracks

21 tracks (168 blocks) of long filemark physical blocks

The information in the filemark physical blocks identifies the filemark’s number and location on the tape and cannot be accessed or changed by the user. The gap tracks at the beginning and end allow file append and file splice operations. The tape drive may write additional gap tracks and gap blocks before the filemark to ensure that all data has been written to tape correctly or to complete tracks that are not completely filled with data blocks.

May 1994	EXB-8205 and EXB-8505	2-17
	(Standard and XL)