fms - Determine a tape's capacity and a tape device's filemark size


fms -tape <tape special file> [-help]

fms -t <tape special file> [-h]


The fms command determines the capacity of the tape currently in the tape device identified by the -tape argument, along with the size of the filemark for the device. The filemark is also referred to as the device's end-of-file (EOF) marker, and can differ for each combination of tape and tape device.

As the Tape Coordinator writes a dump, it writes a filemark between the data included from each volume and also tracks the amount of space left before the end of the tape (EOT). For some tape devices, the filemark is large enough (multiple megabytes) that failure to consider it leads the Tape Coordinator significantly to overestimate the available space.

The intended use of this command is to determine tape capacity and filemark size values that can be specified in a tape device's entry in the /usr/afs/backup/tapeconfig file. For certain types of tape drives, the Tape Coordinator operates more efficiently when the tapeconfig file lists accurate values. For further discussion, see the OpenAFS Administration Guide chapter on configuring the Backup System.

Insert a tape in the drive before issuing this command.


Do not use this command on compressing tape devices in compression mode or with tape devices that handle tapes of multigigabyte (or multiterabyte) capacity. It does not produce accurate results in those cases. For alternate suggestions on the values to record in the tapeconfig file for compressing drives, see the OpenAFS Administration Guide chapter on configuring the Backup System.

Running the command completely overwrites the tape, so use a blank one or one that can be recycled.

Because it writes filemarks to the complete length of the tape, the command can take from several hours to more than a day to complete.


-tape <tape special file>

Specifies the UNIX device name of the tape device for which to determine filemark size and the capacity of the tape it currently contains. The format varies on different system types, but usually begins with /dev; an example is /dev/sd0a.


Prints the online help for this command. All other valid options are ignored.


The command generates output both on the standard output stream and in the fms.log file that it creates in the current working directory. The output reports the capacity of the tape in the device and the device's filemark size.

The first few lines of output include status information about the execution of the command, including such information as the number of blocks and the number of file marks written to the tape by the command. The last two lines of both screen and file output provide the following information:

The following message indicates that the fms command interpreter cannot access the tape device. The command halts.

   Can't open tape drive I<device>

The following message indicates that the command interpreter cannot create the fms.log log file. Again, the command halts.

   Can't open log file


The following command illustrates the output for the device called /dev/rmt1h:

   % fms /dev/rmt1h
   wrote block: 130408
   Finished data capacity test - rewinding
   wrote 1109 blocks, 1109 file marks
   Finished file mark test
   Tape capacity is 2136604672 bytes
   File marks are 1910205 bytes

The following appears in the fms.log file:

   fms test started
   wrote 9230 blocks
   Finished file mark test
   Tape capacity is 151224320 bytes
   File marks are 2375680 bytes


The issuer must be able to insert and write to files in the currently working directory, if the fms.log file does not already exist. If it already exists, the issuer need only be able to write to it.


fms.log(5), tapeconfig(5)


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