Fibre Channel disk subsystem
73
Symmetrix DMX-3 Hardware
Figure 12 Track format for 3390 DASD
Track format
All tracks are written with formatted records. The start and end of
each track are defined by the index marker. Each track has the same
basic format as that shown in Figure 12 on page 73. That is, it has an
index marker, home address (HA), record zero (R0), and one or more
data records (R1 through Rn). These track formats are discussed in
the following sections.
Information is recorded on all Symmetrix disk drives in an emulation
format chosen at configuration. Each track contains certain nondata
information (such as the address of the track, the address of each
record, the length of each record, and the gaps between each area),
and data information.
Index marker — An index marker indicates the physical beginning
and end of each track for each disk drive (Figure 12 on page 73).
Home address (HA) — There is one home address on each track that
defines the physical location of the track by specifying the track
address (cylinder and head location) and the condition of the track
(flag byte). The flag byte indicates whether the track is usable,
defective, or an alternate track.
Record zero–r0 (track descriptor record) — This is the first record
after the home address. The Count field indicates its physical location
(cylinder and head), record number, key length, and data length. In
general, the key length is zero bytes and the data length is eight.
Data records (R1 through Rn) — All remaining records on a track are
data records. The Count field indicates the data record's physical
location (cylinder and head), record number, key length, and data
length. The key is optional and, when used, contains information
used by an application. The data area contains the user data. To
determine the number of records a track can hold, refer to the IBM
3390 Direct Access Storage Introduction or IBM 3380 Direct Access
Storage Introduction for the equations for calculating this number.
Index
marker
HA D
R1
KCD
Magnetic
disk
KC
R0
Index
marker
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