This section describes how to use the dump command with DAT media, and discusses audio and video storage capacities of DAT media.
The dump command backs up all files in a filesystem, or files changed after a certain date, to magnetic tape or files.
If you are using the dump command to perform an incremental filesystem dump with a DAT tape drive, reduce the 4-mm tape-length parameter by 40 percent for the 60-meter DAT tape, and leave as is for the 90-meter tape (2.0 gigabytes). Trim an additional 5 or 10 percent if you want to be conservative.
This section presents formulas and examples you can use to help determine audio and video storage capacities for your DAT tape.
To calculate audio storage capacity, use the following formula:
(sample rate) (sample size) (channels) ¸ (bits per byte) = data rate
For example,
(44100 Hz) (16 bit unsigned) (2 for stereo) ¸ (8 bits per byte) = 176400 bytes/sec = 10.6 MB/min
For video and movie storage, use this formula:
(bits per pixel) (pixels per frame) (frame rate) ¸ (bits per byte) = data rate
For example,
(16 bit YCrCb) (640x480 NTSC-ready frame) (30 fps) ¸ (8 bits per byte) = 18.4 MB/sec
The examples given assume high-quality media; your rates may be less depending on the quality of media you use. You should see about two minutes of music per meter of DAT tape. With video, a 1300 MB DAT stores about 60 seconds of uncompressed video (8-bit CCIR601 4:2:2 frames) and about 144 minutes of MPEG-1 movie (audio and video). Most popular video or movie compression software algorithms fall somewhere between uncompressed video and MPEG-1 (QuickTime, AVI, and so on.) Refer to manufacturer and standards documentation for the latest information.
Note: IRIX supports playback of audio from DAT but does not support playback of video from DAT. You cannot, for example, store an MPEG movie on DAT and then play the movie using the DAT drive.