Guralp Systems CMG-DCM - Manual (Page 116)

CMG-DCM Data Communications Module
8.1 File systems
The DCM uses the standard Unix/Linux file naming conventions. The
operating system resides in two blocks of Flash memory, mounted on /
and /boot; when the module is powered up, a separate boot loader
loads the rest of the operating system.
Once the operating system is loaded, the main Flash memory blocks
(where present) are mounted on /nand0 and /nand1. Incoming data,
which may be from several sources, is combined into a single stream
and placed in one of these blocks (whichever is less full). When in use,
you can expect each to be between 50% and 75% full, with several
da:ta files present. If the DCM is using GCF as its storage file format
(recommended; see Section 6.3, page 86) then each file will be named
after the timestamp on its first packet of data, in the following fashion:
file-yyyymmdd-jjj-s-cccccccc.gcf where yyyymmdd
represents the date of the earliest data packet in the file, jjj the
number of full days elapsed since midnight on January 1, s the time
segment within the day (each day is divided into eight 3-hour
segments), and cccccccc a unique hexadecimal code included to
ensure filenames do not coincide.
When one of the Flash memory blocks approaches capacity, or after a
fixed time period (if you have configured it to do this) the DCM will
automatically move them onto the primary USB hard disk. This may
be either an internal Lacie hard disk, or an external drive connected to
the module through a USB client interface. This disk uses a specially-
designed journalled filesystem, which is designed to maintain the
integrity of your data at all times. Even if a write operation fails or is
aborted suddenly, the disk will still contain a valid filesystem with all
previously-saved data intact, which can be read using any driver that
supports FAT32.
There is a set of specialised commands which allow you to perform
basic tasks on this filesystem:
gfat32df : Displays the size of the filesystem, and how much free
space remains, in a format similar to this:
FAT32 filesystem has 15 G bytes free
Partition is 37 G bytes (78140097 blocks of 512 bytes)
If no suitable storage medium can be found, you will see the message
Failed to find a USB disk.
diskman : Ensures that the /nandx partitions do not become full by
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