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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 2-2 shows the type and size of filemarks for each
format type.
Tape format
Type and size of filemarks
Long filemark
(KBytes)
Short filemark
(KBytes)
8500 or
8500c
48 1
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.
Table 2-2 Type and size of filemarks for each format
May 1994 EXB-8205 and EXB-8505 2-17
(Standard and XL)
2 Recording Format