Guralp Systems CMG-SAM - Manual (Page 15)

Operator’s Guide CMG SAM & CMG CRM
2.5 CHANGING S.C.S.I. DISCS
The 4 channel system takes approximately 25 minutes to fill the silicon buffer (8Mb)
and then about 10 minutes to transfer the data to disc. The disc should preferably be
changed during the period that it is not being accessed to avoid loss of data - if the disc
is switched off and removed during the backup time no data is lost as long as there is
still space available in the silicon file. When the disc is reinstalled backup will
recommence when the silicon file is once again 15/16ths full.
The disc status bargraph indicates disc usage in the same manner. For a 1 Gb disc each
1/16th segment is approximately 64 Mb. Ideally the disc should be replaced when all
LEDs are lit, indicating less than 64 Mb of space remaining. When the disc is
completely full no more data is written to disc and the silicon file buffer will start to
lose the oldest data. This situation is indicated by all 4 of the disc LEDs flashing
simultaneously.
Whenever the disc key lock is turned to remove the disc the system indicates this state
by alternately flashing the disc status LEDs (1+4 & 2+8). When the disc is reinstalled
and the key lock closed the system automatically powers up the disc, indicated by the
‘walking’ LEDs and the ‘access’ lamp illuminating, and checks the FAT for the disc
identity and space available.
If the disc-ID is different from the system-ID the FAT (File Allocation Table) will be
initialised and the disc treated as empty so the disc status will show empty (no LEDS).
If the disc-ID matches the system-ID the space used will be shown on the disc bargraph
and the system will continue to use this disc until full.
Thus to reuse a disc once the data has been retrieved the first location in the FAT should
be erased, or discs can be used in another SAM which would have a non-matching
disc/system-ID.
Issue D March 2001 13