To use many of the features that automate backup operations, create a configuration file for each tape device in the /usr/afs/backup directory on the local disk of the Tape Coordinator machine that drives the device. The filename has the following form:

CFG_device_name

where device_name represents the name of the tape device or backup data file (see Dumping Data to a Backup Data File to learn about writing dumps to a file rather than to tape).

For a tape device, construct the device_name portion of the name by stripping off the initial /dev/ string with which all UNIX device names conventionally begin, and replacing any other slashes in the name with underscores. For example, CFG_rmt_4m is the appropriate filename for a device called /dev/rmt/4m.

For a backup data file, construct the device_name portion by stripping off the initial slash (/) and replacing any other slashes (/) in the name with underscores. For example, CFG_var_tmp_FILE is the appropriate filename for a backup data file called /var/tmp/FILE.

Creating a device configuration file is optional. If you do not want to take advantage of any of the features that the file provides, you do not have to create it.

You can include one of each of the following instructions in any order in a device configuration file. All are optional. Place each instruction on its own line, but do not include any newline (<Return>) characters within an instruction.

A tape stacker or jukebox helps you automate backup operations because it can switch between multiple tapes during an operation without human intervention. To take advantage of this feature, include the MOUNT and optionally UNMOUNT instructions in the device configuration file that you write for the stacker or jukebox. The instructions share the same syntax:

MOUNT filename
   UNMOUNT filename

where filename is the pathname on the local disk of a script or program you have written that invokes the routines defined by the device's manufacturer for mounting or unmounting a tape in the device's tape drive. (For convenience, the following discussion uses the term script to refers to both scripts and programs.) The script usually also contains additional logic that handles error conditions or modifies the script's behavior depending on which backup operation is being performed.

You can refer to different scripts with the MOUNT or UNMOUNT instructions, or to a single script that invokes both mounting and unmounting routines. The scripts inherit the local identity and AFS tokens associated with to the issuer of the butc command.

You need to include a MOUNT instruction in the device configuration file for all tape devices, but the need for an UNMOUNT instruction depends on the tape-handling routines that the device's manufacturer provides. Some devices, usually stackers, have only a single routine for mounting tapes, which also automatically unmounts a tape whose presence prevents insertion of the required new tape. In this case, an UNMOUNT instruction is not necessary. For devices that have separate mounting and unmounting routines, you must include an UNMOUNT instruction to remove a tape when the Tape Coordinator is finished with it; otherwise, subsequent attempts to run the MOUNT instruction fail with an error.

When the device configuration file includes a MOUNT instruction, you must stock the stacker or jukebox with the necessary tapes before running a backup operation. Many jukeboxes are able to search for the required tape by reading external labels (such as barcodes) on the tapes, but many stackers can only switch between tapes in sequence and sometimes only in one direction. In the latter case, you must also stock the tapes in the correct order.

To obtain a list of the tapes required for a restore operation so that you can prestock them in the tape device, include the -n flag on the appropriate backup command (backup diskrestore, backup volrestore, or backup volsetrestore). For a dump operation, it is generally sufficient to stock the device with more tapes than the operation is likely to require. You can prelabel the tapes with permanent names or AFS tape names, or not prelabel them at all. If you prelabel the tapes for a dump operation with AFS tape names, then it is simplest to load them into the stacker in sequential order by tape index. But it is probably simpler still to prelabel tapes with permanent tape names or use unlabeled tapes, in which case the Backup System generates and applies the appropriately indexed AFS tape name itself during the dump operation.

   #! /bin/csh -f
   set devicefile = $1
   set operation = $2
   set tries = $3
   set tapename = $4
   set tapeid = $5
   set exit_continue = 0
   set exit_abort = 1
   set exit_interactive = 2
   #--------------------------------------------
   if (${tries} > 1) then
      echo "Too many tries"
      exit ${exit_interactive}
   endif
   if (${operation} == "unmount") then
      echo "UnMount: Will leave tape in drive"
      exit ${exit_continue}
   endif
   if ((${operation} == "dump")     |\
       (${operation} == "appenddump")     |\
       (${operation} == "savedb"))  then
       stackerCmd_NextTape ${devicefile}
       if (${status} != 0)exit${exit_interactive}
       echo "Will continue"
       exit ${exit_continue}
   endif
   if ((${operation} == "labeltape")    |\
       (${operation} == "readlabel")) then
      echo "Will continue"
      exit ${exit_continue}
   endif
   echo "Prompt for tape"
   exit ${exit_interactive}

By default, the Tape Coordinator obtains the first tape it needs for a backup operation by reading the device configuration file for the appropriate tape device. If there is a MOUNT instruction in the file, the Tape Coordinator executes the referenced script. If the device configuration file does not exist or does not have a MOUNT instruction in it, the Tape Coordinator prompts you to insert the correct tape and press <Return>.

If you know in advance that an operation requires a tape, you can increase efficiency by placing the required tape in the drive before issuing the backup command and telling the Tape Coordinator's to skip its initial tape-acquisition steps. This both enables the operation to begin more quickly and eliminates that need for you to be present to insert a tape.

There are two ways to bypass the Tape Coordinator's initial tape-acquisition steps:

To avoid any error conditions that require operator attention, be sure that the tape you are placing in the drive does not contain any unexpired dumps and is not write protected. If there is no permanent name on the tape's label and you are creating an initial dump, make sure that the AFS tape name either matches the volume set and dump set names or is <NULL>. Alternatively, suppress the Tape Coordinator's name verification step by assigning the value NO to the NAME_CHECK instruction in the device configuration file, as described in Eliminating the AFS Tape Name Check.

By default, the Tape Coordinator asks you how to respond when it encounters certain error conditions. To suppress the prompts and cause the Tape Coordinator to handle the errors in a predetermined manner, include the instruction ASK NO in the device configuration file. If you assign the value YES, or omit the ASK instruction completely, the Tape Coordinator prompts you for direction when it encounters one of the errors.

The following list describes the error conditions and the Tape Coordinator's response to them.

If a tape does not have a permanent name and you are writing an initial dump to it, then by default the Backup System verifies that the tape's AFS tape name is acceptable. It accepts three types of values:

To bypass the name check, include the NAME_CHECK NO instruction in the device configuration file. This enables you to recycle a tape without first relabeling it, as long as all dumps on it are expired. (If a tape has unexpired dumps on it but you want to recycle it anyway, you must use the backup labeltape command to relabel it first. For this to work, the ASK NO instruction cannot appear in the device configuration file.)

By default, the Tape Coordinator uses a 16-KB memory buffer during dump operations. As it receives volume data from the Volume Server, the Tape Coordinator gathers 16 KB of data in the buffer before transferring the entire 16 KB to the tape device. Similarly, during a restore operation the Tape Coordinator by default buffers 32 KB of data from the tape device before transferring the entire 32 KB to the Volume Server for restoration into the file system. Buffering makes the volume of data flowing to and from a tape device more even and so promotes tape streaming, which is the most efficient way for a tape device to operate.

In a normal network configuration, the default buffer sizes are usually large enough to promote tape streaming. If the network between the Tape Coordinator machine and file server machines is slow, it can help to increase the buffer size.

To determine if altering the buffer size is helpful for your configuration, observe the tape device in operation to see if it is streaming, or consult the manufacturer. To set the buffer size, include the BUFFERSIZE instruction in the device configuration file. It takes an integer value, and optionally units, in the following format:

BUFFERSIZE size[{k | K | m | M | g | G}]

where size specifies the amount of memory the Tape Coordinator allocates to use as a buffer during both dump and restore operations. The default unit is bytes, but use k or K to specify kilobytes, m or M for megabytes, and g or G for gigabytes. There is no space between the size value and the units letter.

You can write dumps to a backup data file rather than to tape. This is useful if, for example, you want to transfer the data to a data-archiving system, such as a hierarchical storage management (HSM) system, that you use in conjunction with AFS and the Backup System. You can restore data from a backup data file into the file system as well. Using a backup data file is usually more efficient than issuing the equivalent vos dump and vos restore commands individually for multiple volumes.

Writing to a backup data file is simplest if it is on the local disk of the Tape Coordinator machine, but you can also write the file to an NFS-mounted partition that resides on a remote machine. It is even acceptable to write to a file in AFS, provided that the access control list (ACL) on its parent directory grants the necessary permissions, but it is somewhat circular to back up AFS data into AFS itself.

If the backup data file does not already exist when the Tape Coordinator attempts to write a dump to it, the Tape Coordinator creates it. For a restore operation to succeed, the file must exist and contain volume data previously written to it during a backup dump operation.

When writing to a backup data file, the Tape Coordinator writes data at 16 KB offsets. If a given block of data (such as the marker that signals the beginning or end of a volume) does not fill the entire 16 KB, the Tape Coordinator still skips to the next offset before writing the next block. In the output of a backup dumpinfo command issued with the -id option, the value in the Pos column is the ordinal of the 16-KB offset at which the volume data begins, and so is not generally only one higher than the position number on the previous line, as it is for dumps to tape.

Before writing to a backup data file, you need to configure the file as though it were a tape device.

You do not need to create the backup data file itself, because the Tape Coordinator does so if the file does not exist when the dump operation begins.

The following example script illustrates how you can automatically create a symbolic link to the backup data file during the preparation phase for writing to the file. When the Tape Coordinator is executing a backup dump, backup restore, backup savedb, or backup restoredb operation, the routine invokes the UNIX ln -s command to create a symbolic link from the backup data file named in the tapeconfig file to the actual file to use (this is the recommended method). It uses the values of the tapename and tapeid parameters passed to it by the Backup System when constructing the filename.

The routine makes use of two other parameters as well: tries and operation. The tries parameter tracks how many times the Tape Coordinator has attempted to access the file. A value greater than one indicates that the Tape Coordinator cannot access it, and the routine returns exit code 2 (exit_interactive), which results in a prompt for the operator to load a tape. The operator can use this opportunity to change the name of the backup data file specified in the tapeconfig file.

   #! /bin/csh -f
   set devicefile = $1
   set operation = $2
   set tries = $3
   set tapename = $4
   set tapeid = $5
   set exit_continue = 0
   set exit_abort = 1
   set exit_interactive = 2
   #--------------------------------------------
   if (${tries} > 1) then
      echo "Too many tries"
      exit ${exit_interactive}
   endif
   if (${operation} == "labeltape") then
      echo "Won't label a tape/file"
      exit ${exit_abort}
   endif
   if ((${operation} == "dump")   |\
       (${operation} == "appenddump")   |\
       (${operation} == "restore")   |\
       (${operation} == "savedb")    |\
       (${operation} == "restoredb")) then
      /bin/rm -f ${devicefile}
      /bin/ln -s /hsm/${tapename}_${tapeid} ${devicefile}
      if (${status} != 0) exit ${exit_abort}
   endif
   exit ${exit_continue}