Specifications

9.3 Recovery from power failure
9.3.1 Power Failure
If a power failure occurs during a record operation, MDR provides a functionality to re-
cover recording data. The MDR system is able to recover the recording data saved to the
MDR disk subsystem if tags are inserted into the recording (insertion of tag is covered in
a later paragraph).
The detection of power failure and the data recovery are carried out automatically during
the boot sequence of the MDR:
• If the MDR detects that a record operation was carried out without using tag inser-
tion then, in order to save any possibly recorded data, the recording is set as stored
(and recorded) by the MDR.
In this case, the last part of the recording may contain valid data
and/or garbage data. The user shall determine the valid recording data.
• If the MDR detects that a record operation was carried out using tag insertion then
the following operations are executed:
1. The number of valid recorded blocks is computed (using the tag information in-
serted inside the recording data),
2. The recording is resized according to the number of recorded blocks found.
Therefore, the recording contains only valid data (no garbage data). The rest of
the data on the MDR disk subsystem may be retrieved using the
ReadRecorder-
Block
function,
3. The recording is set as
stored and recorded.
9.3.2 Tag Insertion
The MDR system is able to insert tags inside the recording data during a record opera-
tion (in both standard and infinite mode).
Each tag is a 512-byte structure containing:
• The MDR identification value (also called magic number),
• The recorder block number,
• The validity of the recorder block,
• Reserved space.
There are two different ways of enabling the tag insertion for a recording:
• During the creation of a recording,
• After the creation of a recording.
The space used by the recording tags is added to the recording user size
(not allocated inside the recording user size). Therefore, more recorder
blocks may be required for a recording with tags (compared to the
same recording without tags).
MDR User Guide 69
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