Disk File System - Northern Telecom DMS-100 Series Maintenance Manual

2-8 DPP system operation

Disk file system

The disk drives provide an off-line medium for data storage unaffected by
power outage. Data remains on disk, as secondary AMA data, even after
polling by the HOC. Due to the large storage capacity of disks, several days
of records are accommodated on the disk, available as backup records to
retrieve at a later time, if necessary. When certain threshold values are
reached, or if additional storage space is required, files are removed from
disk. Sufficient disk capacity allows several days storage while polling
problems are resolved, so that no data is lost.
The DPP uses a redundant disk configuration which can operate in either a
prime or only mode. The prime mode is the normal operating mode for the
disk system. In the prime mode, data is written to both disks; first to the
prime disk, then the standby disk. In the only mode, data is written to only
one disk. The only mode is used when either disk drive is unavailable due
to a fault, or some maintenance condition.
The DPP disk system consists of multiple files. The maximum number of
files is 192 for 70 and 140 Mbyte disk drives, 383 for 380 Mbyte disk
drives, and 511 for 760-Mbyte disk drives. These files can be displayed by
use of the LSTDIR ALL command. For more information concerning the
LSTDIR command, consult 297-1001-821.
The total number of files divides into two categories: static, and dynamic.
Dynamic files are usually large, while most static files are small. Most
dynamic files are data files, consisting of (AMA), exception (EXC), and log
records. Each of these files has an index file associated with it. Static files
are stand-alone files, which are primarily various index files that are used for
the management of data, statistics, site data, program, boot, and other files.
Due to DPR buffer limitations, only 14 files can be open (reading from or
writing to) at one time. This is further divided into seven dynamic and
seven static files. Since only seven dynamic files may be open at one time,
this is the total number of data files that may be polled from or written to at
one time. The data files may have a maximum of 255 versions, after which
it rolls back to restart the count at version 1, with the previous version 1
deleted.
The maximum number of AMA blocks in any one file version is disk-size
dependent, as follows:
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•
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297-1001-537 Standard 01.02 December 1993
Note: File versions containing primary data are not deleted.
72- and 140-Mbyte disk drives
380-Mbyte w/o 56K polling
380- and 760-Mbyte w/56K polling
945 blocks/version
3836 blocks/version
4780 blocks/version