butc(5)
NAME
butc - Defines Tape Coordinator instructions for automated tape devices
DESCRIPTION
The CFG_device_name file includes instructions that configure a Tape
Coordinator (butc) for use with automated backup devices such as tape
stackers and jukeboxes, enable the Tape Coordinator to dump and restore
data to a backup data file on a local disk device, and enable greater
automation of other aspects of the backup process.
There is a separate configuration file for each tape device or backup
data file. Creating the file is optional, and unnecessary if none of
the instructions it can include pertain to a given tape device. The
ASCII-format file must reside in the /var/lib/openafs/backup directory
on the Tape Coordinator machine if it exists.
The CFG_device_name file does not replace the
/var/lib/openafs/backup/tapeconfig file, a single copy of which still
must exist on every Tape Coordinator machine.
To enable the Tape Coordinator to locate the configuration file,
construct the variable part of the filename, device_name, as follows:
* For a tape device, strip off the initial "/dev/" string from the
device name, and replace 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, strip off the initial slash ("/") and
replace 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.
The CFG_device_name file lists one or more of the following
instructions, each on its own line. All are optional, and they can
appear in any order. A more detailed description of each instruction
follows the list:
ASK Controls whether the Tape Coordinator prompts for guidance when it
encounters error conditions.
AUTOQUERY
Controls whether the Tape Coordinator prompts for the first tape.
BUFFERSIZE
Sets the size of the memory buffer the Tape Coordinator uses when
transferring data.
FILE
Controls whether the dump is written to a tape device or a file.
MOUNT
Identifies the file that contains routines for inserting tapes into
the device's drive.
NAME_CHECK
Controls whether the Tape Coordinator verifies that a tape's AFS
tape name matches the dump being written.
UNMOUNT
Identifies the file that contains routines for removing tapes from
the device's drive.
The ASK Instruction
The "ASK" instruction takes a boolean value as its argument, in the
following format:
ASK (YES | NO)
When the value is "YES", the Tape Coordinator generates a prompt in its
window, requesting a response to the error cases described in the
following list. This is the default behavior if the "ASK" instruction
does not appear in the CFG_device_name file.
When the value is "NO", the Tape Coordinator does not prompt in error
cases, but instead uses the automatic default responses described in
the following list. The Tape Coordinator also logs the error in the
TE_device_name file. Suppressing the prompts enables the Tape
Coordinator to run unattended, though it still prompts for insertion of
tapes unless the "MOUNT" instruction is used.
The error cases controlled by this instruction are the following:
* The Backup System is unable to dump a volume while running the
backup dump command. With a "YES" value, the Tape Coordinator
prompts to offer three choices: try to dump the volume again
immediately, omit the volume from the dump but continue the
operation, or terminate the operation. With a "NO" value, the Tape
Coordinator omits the volume from the dump and continues the
operation.
* The Backup System is unable to restore a volume while running the
backup diskrestore, backup volrestore, or backup volsetrestore
command. With a "YES" value, the Tape Coordinator prompts to offer
two choices: omit the volume and continue restoring the other
volumes, or terminate the operation. With a "NO" value, it
continues the operation without prompting, omitting the problematic
volume but restoring the remaining ones.
* The Backup System cannot determine if the dump set includes any
more tapes, while running the backup scantape command (the
reference page for that command discusses possible reasons for this
problem). With a "YES" value, the Tape Coordinator prompts to ask
if there are more tapes to scan. With a "NO" value, it proceeds as
though there are more tapes and invokes the routine named by the
"MOUNT" instruction in the configuration file, or prompts the
operator to insert the next tape.
* The Backup System determines that the tape contains an unexpired
dump while running the backup labeltape command. With a "YES"
value, the Tape Coordinator prompts to offer two choices: continue
or terminate the labeling operation. With a "NO" value, it
terminates the operation without relabeling the tape.
The AUTOQUERY Instruction
The "AUTOQUERY" instruction takes a boolean value as its argument, in
the following format:
AUTOQUERY (YES | NO)
When the value is "YES", the Tape Coordinator checks for the "MOUNT"
instruction in the configuration file when it needs to read the first
tape involved in an operation. As described for that instruction, it
then either prompts for the tape or invokes the specified routine to
mount the tape. This is the default behavior if the "AUTOQUERY"
instruction does not appear in the configuration file.
When the value is "NO", the Tape Coordinator assumes that the first
tape required for an operation is already in the drive. It does not
prompt the operator or invoke the "MOUNT" routine unless there is an
error in accessing the first tape. This setting is equivalent in effect
to including the -noautoquery flag to the butc command.
Note that the setting of the "AUTOQUERY" instruction controls the Tape
Coordinator's behavior only with respect to the first tape required for
an operation. For subsequent tapes, the Tape Coordinator always checks
for the "MOUNT" instruction. It also refers to the "MOUNT" instruction
if it encounters an error while attempting to access the first tape.
The BUFFERSIZE Instruction
The "BUFFERSIZE" instruction 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.
By default, the Tape Coordinator uses a 16 KB 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 or backup data file. Similarly, during
a restore operation the Tape Coordinator by default buffers 32 KB of
data from the tape device or backup data file 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.
The FILE Instruction
The "FILE" instruction takes a boolean value as its argument, in the
following format:
FILE (NO | YES)
When the value is "NO", the Tape Coordinator writes to a tape device
during a dump operation and reads from one during a restore operation.
This is the default behavior if the "FILE" instruction does not appear
in the configuration file.
When the value is "YES", the Tape Coordinator writes volume data to a
backup data file on the local disk during a dump operation and reads
volume data from a file during a restore operation. If the file does
not exist when the Tape Coordinator attempts to access it to write a
dump, the Tape Coordinator creates it. For a restore operation to
succeed, the file must exist and contain volume data previously written
to it by a backup dump operation.
When the value is "YES", the backup data file's complete pathname must
appear (instead of a tape drive device name) in the third field of the
corresponding port offset entry in the local
/var/lib/openafs/backup/tapeconfig file. If the field instead refers to
a tape device, dump operations appear to succeed but are inoperative.
It is not possible to restore data that was accidently dumped to a tape
device while the "FILE" instruction was set to "YES". (In the same way,
if the "FILE" instruction is set to "NO", the tapeconfig entry must
refer to an actual tape device.)
Rather than put an actual file pathname in the third field of the
tapeconfig file, however, the recommended configuration is to create a
symbolic link in the /dev directory that points to the actual file
pathname, and record the symbolic link in this field. This
configuration has a couple of advantages:
* It makes the device_name portion of the CFG_device_name,
TE_device_name, and TL_device_name names as short as possible.
Because the symbolic link is in the /dev directory as though it
were a tape device, the device configuration file's name is
constructed by stripping off the entire /dev/ prefix, instead of
just the initial slash. If, for example, the symbolic link is
called /dev/FILE, the device configuration file name is CFG_FILE,
whereas if the actual pathname /var/tmp/FILE appears in the
tapeconfig file, the file's name must be CFG_var_tmp_FILE.
* It provides for a more graceful, and potentially automated,
recovery if the Tape Coordinator cannot write a complete dump into
the backup data file (because the partition housing the backup data
file becomes full, for example). The Tape Coordinator's reaction to
this problem is to invoke the "MOUNT" script, or to prompt the
operator if the "MOUNT" instruction does not appear in the
configuration file.
* If there is a "MOUNT" routine, the operator can prepare for
this situation by adding a subroutine that changes the symbolic
link to point to another backup data file on a partition where
there is space available.
* If there is no "MOUNT" instruction, the prompt enables the
operator manually to change the symbolic link to point to
another backup data file, then press Return to signal that the
Tape Coordinator can continue the operation.
If the third field in the tapeconfig file names the actual file, there
is no way to recover from exhausting the space on the partition that
houses the backup data file. It is not possible to change the
tapeconfig file in the middle of an 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.
The MOUNT Instruction
The "MOUNT" instruction takes a pathname as its argument, in the
following format:
MOUNT <filename>
The referenced executable file must reside on the local disk and
contain a shell script or program that directs an automated tape
device, such as a jukebox or stacker, to mount a tape (insert it into
the tape reader). The operator must write the routine to invoke the
mount command specified by the device's manufacturer; AFS does not
include any scripts, although an example appears in "EXAMPLES". The
script or program inherits the Tape Coordinator's AFS authentication
status.
When the Tape Coordinator needs to mount a tape, it checks the
configuration file for a "MOUNT" instruction. If there is no "MOUNT"
instruction, the Tape Coordinator prompts the operator to insert a tape
before it attempts to open the tape device. If there is a "MOUNT"
instruction, the Tape Coordinator executes the routine in the
referenced file. The routine invoked by the "MOUNT" instruction
inherits the local identity (UNIX UID) and AFS tokens of the butc
command's issuer.
There is an exception to this sequence: if the "AUTOQUERY NO"
instruction appears in the configuration file, or the -noautoquery flag
was included on the butc command, then the Tape Coordinator assumes
that the operator has already inserted the first tape needed for a
given operation. It attempts to read the tape immediately, and only
checks for the "MOUNT" instruction or prompts the operator if the tape
is missing or is not the required one.
When the Tape Coordinator invokes the routine indicated by the "MOUNT"
instruction, it passes the following parameters to the routine in the
indicated order:
* The tape device or backup data file's pathname, as recorded in the
/var/lib/openafs/backup/tapeconfig file.
* The tape operation, which (except for the exceptions noted in the
following list) matches the backup command operation code used to
initiate the operation:
* "appenddump" (when a backup dump command includes the -append
flag).
* "dump" (when a backup dump command does not include the -append
flag).
* "labeltape"
* "readlabel"
* "restore" (for a backup diskrestore, backup volrestore, or
backup volsetrestore command).
* "restoredb"
* "savedb"
* "scantape"
* The number of times the Tape Coordinator has attempted to open the
tape device or backup data file. If the open attempt returns an
error, the Tape Coordinator increments this value by one and again
invokes the "MOUNT" instruction.
* The tape name. For some operations, the Tape Coordinator passes the
string "none", because it does not know the tape name (when running
the backup scantape or backup readlabel, for example), or because
the tape does not necessarily have a name (when running the backup
labeltape command, for example).
* The tape ID recorded in the Backup Database. As with the tape name,
the Backup System passes the string "none" for operations where it
does not know the tape ID or the tape does not necessarily have an
ID.
The routine invoked by the "MOUNT" instruction must return an exit code
to the Tape Coordinator:
* Code 0 (zero) indicates that the routine successfully mounted the
tape. The Tape Coordinator continues the backup operation. If the
routine invoked by the "MOUNT" instruction does not return this
exit code, the Tape Coordinator never calls the "UNMOUNT"
instruction.
* Code 1 (one) indicates that the routine failed to mount the tape.
The Tape Coordinator terminates the operation.
* Any other code indicates that the routine was not able to access
the correct tape. The Tape Coordinator prompts the operator to
insert the correct tape.
If the backup command was issued in interactive mode and the operator
issues the backup kill command while the "MOUNT" routine is running,
the Tape Coordinator passes the termination signal to the routine; the
entire operation terminates.
The NAME_CHECK Instruction
The "NAME_CHECK" instruction takes a boolean value as its argument, in
the following format:
NAME_CHECK (YES | NO)
When the value is "YES" and the tape does not have a permanent name,
the Tape Coordinator checks the AFS tape name when dumping a volume in
response to the backup dump command. The AFS tape name must be "<NULL>"
or match the tape name that the backup dump operation assigns based on
the volume set and dump level names. This is the default behavior if
the "NAME_CHECK" instruction does not appear in the configuration file.
When the value is "NO", the Tape Coordinator does not check the AFS
tape name before writing to the tape.
The Tape Coordinator always checks that all dumps on the tape are
expired, and refuses to write to a tape that contains unexpired dumps.
The UNMOUNT Instruction
The "UNMOUNT" instruction takes a pathname as its argument, in the
following format:
UNMOUNT <filename>
The referenced executable file must reside on the local disk and
contain a shell script or program that directs an automated tape
device, such as a jukebox or stacker, to unmount a tape (remove it from
the tape reader). The operator must write the routine to invoke the
unmount command specified by the device's manufacturer; AFS does not
include any scripts, although an example appears in "EXAMPLES". The
script or program inherits the Tape Coordinator's AFS authentication
status.
After closing a tape device, the Tape Coordinator checks the
configuration file for an "UNMOUNT" instruction, whether or not the
close operation succeeds. If there is no "UNMOUNT" instruction, the
Tape Coordinator takes no action, in which case the operator must take
the action necessary to remove the current tape from the drive before
another can be inserted. If there is an "UNMOUNT" instruction, the Tape
Coordinator executes the referenced file. It invokes the routine only
once, passing in the following parameters:
* The tape device pathname (as specified in the
/var/lib/openafs/backup/tapeconfig file).
* The tape operation (always unmount).
PRIVILEGE REQUIRED
The file is protected by UNIX mode bits. Creating the file requires the "w" (write) and "x" (execute) permissions on the /var/lib/openafs/backup directory. Editing the file requires the "w" (write) permission on the file.
EXAMPLES
The following example configuration files demonstrate one way to
structure a configuration file for a stacker or backup dump file. The
examples are not necessarily appropriate for a specific cell; if using
them as models, be sure to adapt them to the cell's needs and
equipment.
Example CFG_device_name File for Stackers
In this example, the administrator creates the following entry for a
tape stacker called "stacker0.1" in the
/var/lib/openafs/backup/tapeconfig file. It has port offset 0.
2G 5K /dev/stacker0.1 0
The administrator includes the following five lines in the
/var/lib/openafs/backup/CFG_stacker0.1 file. To review the meaning of
each instruction, see "DESCRIPTION".
MOUNT /var/lib/openafs/backup/stacker0.1
UNMOUNT /var/lib/openafs/backup/stacker0.1
AUTOQUERY NO
ASK NO
NAME_CHECK NO
Finally, the administrator writes the following executable routine in
the /var/lib/openafs/backup/stacker0.1 file referenced by the "MOUNT"
and "UNMOUNT" instructions in the CFG_stacker0.1 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} == "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}
This routine uses two of the parameters passed to it by the Backup
System: "tries" and "operation". It follows the recommended practice of
prompting for a tape if the value of the "tries" parameter exceeds one,
because that implies that the stacker is out of tapes.
For a backup dump or backup savedb operation, the routine calls the
example "stackerCmd_NextTape" function provided by the stacker's
manufacturer. Note that the final lines in the file return the exit
code that prompts the operator to insert a tape; these lines are
invoked when either the stacker cannot load a tape or a the operation
being performed is not one of those explicitly mentioned in the file
(such as a restore operation).
Example CFG_device_name File for Dumping to a Data File
In this example, the administrator creates the following entry for a
backup data file called HSM_device in the
/var/lib/openafs/backup/tapeconfig file. It has port offset 20.
1G 0K /dev/HSM_device 20
The administrator includes the following lines in the
/var/lib/openafs/backup/CFG_HSM_device file. To review the meaning of
each instruction, see "DESCRIPTION".
MOUNT /var/lib/openafs/backup/file
FILE YES
ASK NO
Finally, the administrator writes the following executable routine in
the /var/lib/openafs/backup/file file referenced by the "MOUNT"
instruction in the CFG_HSM_device file, to control how the Tape
Coordinator handles the 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}
Like the example routine for a tape stacker, this routine uses the
"tries" and "operation" parameters passed to it by the Backup System.
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.
The primary function of this routine is to establish a link between the
device file and the file to be dumped or restored. 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 value of the "tapename" and "tapeid" parameters to
construct the file name.
SEE ALSO
tapeconfig(5), backup_diskrestore(8), backup_dump(8), backup_restoredb(8), backup_savedb(8), backup_volrestore(8), backup_volsetrestore(8)
COPYRIGHT
IBM Corporation 2000. <http://www.ibm.com/> All Rights Reserved. This documentation is covered by the IBM Public License Version 1.0. It was converted from HTML to POD by software written by Chas Williams and Russ Allbery, based on work by Alf Wachsmann and Elizabeth Cassell.
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