The original version of LOS could, optionally, duplicate every write to disc onto a second cartridge. The purpose was to ensure a system could continue running (as described below), should one drive fail, by "mirroring" its data in real time onto second drive.
However, this only protected against mechanical drive failure (which proved to be inadequate) so the additional capacity provided by the second drive was soon reassigned for extra data storage.
The two disc drives (units 70 and 71) provide double the on-line disc capacity required during normal operating. To enable operations to continue should one of the drives fail, all data is duplicated on each drive.
The fixed cartridges are Master Discs, labeled 027 and 017. Under normal circumstances programs read from and write to the master discs. The operating system intercepts all writes and duplicates them onto the corresponding Slave disc.
Disc 010 is the Slave of Disc 017, Disc 020 is the Slave of 027.
Note: The Slave cartridge will normally be loaded onto the opposite drive to its Master, but this is not an essential requirement.
Failure is indicated either by the permanent absence of the READY light or by a STATUS message flashed to all VDU's at approximately 20-second intervals.
To withdraw discs from the system:
System resumes with the indicated cartridges withdrawn. If a MASTER has been withdrawn, all read/writes are directed to the SLAVE. If a SLAVE has been withdrawn, it is ignored by the system except if a write was pending when withdrawn it will remain pending (under these circumstances the Slave should be taken off-line to prevent the system from continuing to attempt to complete the write) (the message that the issuing task is still awaiting the Slave may be ignored until repairs have been carried out).
Checkword Errors are usually caused by processor or core faults.
Use programs DS10 and DS20 in parallel as usual.
Use programs DS10 and DS20 one at a time, loading the security cartridge onto the opposite drive to usual and keeping the appropriate slave online.
Use program DS10 only.
At the prompt PHASE 1 ONLY? press REJECT.
Load discs as and when called for. Allow 50 minutes for the whole operation.
Should it become necessary to recover the system from this security, security disc 11 (or 12) must be placed on Unit 70 first. (This cannot be carried out until Unit 70 is repaired, unless the engineer reverses the interface connections.)
Use program DS20 only.
At the prompt PHASE 1 ONLY? press REJECT.
Load discs as and when called for. Allow 50 minutes for the whole operation.
Should it become necessary to recover the system from this security, security disc 21 (or 22) must be placed on Unit 70 first.
Step | Prompt | Action |
---|---|---|
1 | Load discs 10 and 20 onto their usual drives. | |
2 | Check that all VDU’s and all printers are idle. | |
3 | Enter program MEND at any VDU. | |
4 | The VDU will display the current on-line security situation. | |
5 | PROCESS? | Either ACCEPT to go to step 6, or REJECT to return to step 4. |
6 | PASSWORD | Enter Password 1. |
7 | Regeneration of the withdrawn cartridges now proceeds automatically. No VDU or printer may carry out any read/write to any disc whilst regeneration is in progress. Any that attempts to do so will HALT AT 03/0451. | |
8 | The message REGENERATION COMPLETED is flashed to all VDU’s upon completion of MEND. |
Should it become necessary to re-bootstrap the system whilst Master Disc 27 is withdrawn, the correct procedure is to return to the latest security. If, nevertheless, an attempt is made to proceed, the bootstrap will read the System Control Record from Disc 27. Unfortunately, this record will be out of date. The appropriate File Control Block should be temporarily modified to read from Disc 20.