Guralp Systems CMG-DCM - Manual (Page 90)

CMG-DCM Data Communications Module
disk.recordinterval : The DCM writes all the data streams it has been
instructed to record into a file in its Flash memory. With the default
setting active, the system starts a new file every 3 hours, alternating
between the two Flash memory banks (see Section 8.1, page 116.) The
3-hour interval is called a
watch.
For those formats which can only deal with single streams, the DCM
opens a file for each stream, starting a new set of files every watch.
You can make watches shorter by setting disk.recordinterval, which is
expressed in seconds. The options are
•
10800 seconds, or 3 hours;
•
3600 seconds, or 1 hour;
•
1800 seconds, or 30 minutes.
The recording interval needs to be chosen with care, bearing in mind
how you will use the DCM.
•
If files are larger than 25% of the Flash memory capacity, the
DCM may encounter problems, because the disk manager only
starts transferring files when the Flash memory is over 75% full.
If a large file fills up the Flash memory before it is finished, the
DCM's watchdog process may force a reboot.
•
In any case, files recorded by the DCM must never exceed 16
Mb owing to internal limitations.
•
Each recording process keeps files open in Flash memory whilst
it is writing to them. For MiniSEED and SAC files, and also for
GCF files if the disk.recordsplit option is active (see below), a
file is opened for every stream the DCM encounters.
The Linux operating system enforces a limit of 1024 files which
can be open at once.
You will only approach this limit if you are running several
recording processes on a large number of streams. If you do, you
may find that decreasing disk.recordinterval helps.
•
The Flash filesystem can store up to 262144 files. It is unlikely
you will approach this limit under normal conditions.
90 Issue F