From The Open Source Backup Wiki (Amanda, MySQL Backup, BackupPC)

Contents 1 Communication method 2 Command sequence during backup operation 3 Other commands 4 Protocol command reference 4.1 Taper command reply 4.2 Driver/Taper Requests/Replies 5 Command/reply arguments 5.1 Protocol data 5.2 driver command 5.3 taper reply 5.4 LOG 6 algorithm after a part written to tape

Communication method

driver talks via two pipes connected to taper's stdin and stdout. The commands and responses are plain text.

Command sequence during backup operation

• driver initialises taper with: START-TAPER <timestamp> to which taper replies with: TAPE-OK or, for fatal errors, with: TAPE-ERROR [<message>]. For speed up,taper is authorized to scan the library and find a valid tape after it received the START-TAPER command.

• driver can ask taper to copy a file from the holding disk to tape (FILE-WRITE) or directly from a dumper (PORT-WRITE) or exit at the end of the run (QUIT).

• taper responds to the PORT-WRITE command with: PORT <port> which driver should then hand on to dumper in a PORT-DUMP command.

• if taper has no tape in use, it reply with REQUEST-NEW-TAPE.

• If the copy to tape finishes correctly taper replies with DONE.

• If something goes wrong with the tape, taper can ask to continue on a new tape REQUEST-NEW-TAPE (for splited dump only) or it can abort that dump with PARTIAL or FAILED reply

• After any dump that finished in PARTIAL or FAILED with a TAPE-ERROR, the driver must send a NEW-TAPE before issuing another *-WRITE command.

Other commands

• If driver says something that taper doesn't recognise it responds with: BAD-COMMAND <message>
• taper responds to the QUIT command with: QUITING

Protocol command reference

Taper command reply

Reply	Description
TAPE-OK	taper is setup correctly
TAPE-ERROR	Error in setup of the driver
PORT	Reply sent in response to PORT-WRITE command
DONE	Full dump is on the media
PARTIAL	Dump was partially written to the media.
FAILED	Nothing was written to the media
DUMPER-STATUS	Ask driver to send the dumper status
PARTDONE	A complete part is written to tape
REQUEST-NEW-TAPE	Ask driver if it should use a new tape
NEW-TAPE	Will continue on a new found tape
NO-NEW-TAPE	Will not continue on a new tape

DONE/PARTIAL and FAILED reply also contains an INPUT-* an TAPE-* message to denote any error:

Reply	Description
INPUT-GOOD	There was no error with the input.
INPUT-ERROR	There was error with the input.

Reply	Description
TAPE-GOOD	This tape can be use to write another dump.
TAPE-ERROR	Nothing more can fit on that tape.

A result for a successful dump should be: DONE INPUT-GOOD TAPE-GOOD

Driver/Taper Requests/Replies

Driver request		Taper reply	Description
initail setup
START-TAPER	--->
	<---	TAPE-OK	normal taper setup (a tape is available, nothing is written on it)
	<---	TAPE-ERROR	failed taper setup (no tape are available or something else is broken)
file-write setup
FILE-WRITE	--->
	<---	REQUEST-NEW-TAPE	(Optional) ask driver if we should start this dump on a new tape. (driver will send a NEW-TAPE or NO-NEW-TAPE command)
			Will get one part-result for each part written and one global result
port-write setup
PORT-WRITE	--->
	<---	PORT
	<---	REQUEST-NEW-TAPE	(Optional) ask driver if we should start this dump on a new tape. (driver will send a NEW-TAPE or NO-NEW-TAPE command)
			Will continue with one part-result for each part written and one global result
global-result
			Can ask-dumper-status (Should be done if taper detect no error (INPUT-GOOD and TAPE-GOOD)
	<---	DONE INPUT-GOOD TAPE-GOOD	normal protocol for a success
	<---	PARTIAL INPUT-* TAPE-*	protocol for error in data phase (something written to tape)
	<---	FAILED INPUT-* TAPE-*	protocol for error in setup (before something is written to tape)
ask-dumper-status
	<---	DUMPER-STATUS	Ask driver the dumper status
DONE	--->		Dumper succeeded
FAILED	--->		Dumper failed
part-result
	<---	PARTDONE	successfully part written to tape
	<---	REQUEST-NEW-TAPE	We get a tape error, ask the driver if we can use a new tape (driver will send a NEW-TAPE or NO-NEW-TAPE command)
driver don't want the taper to use a new tape
NO-NEW-TAPE	--->		driver doesn't want the taper to use a new tape (continue with global-result)
driver want the taper to use a new tape
NEW-TAPE	--->		driver want the taper to use a new tape
	<---	GOT-NEW-TAPE	taper found one
	<---	NO-NEW-TAPE	no tape are available
quit
QUIT	--->
	<---	QUITING

Command/reply arguments

Protocol data

data	description
<timestamp>	Time as "yymmdd" of "yymmddhhmmss"
<handle>	Request ID
<filename>	Name of file on the holding disk where backup will be written to
<port>	Taper port to send the backup data to
<host>	Hostname of the client
<disk>	Disk on the client being backed up
<level>	Dump level being used for backup
splitsize	size of each part on tape
split_diskbuffer	file use to buffer a complete part
<message>	Error or Status message

driver command

• START-TAPER timestamp
• PORT-WRITE handle hostname diskname level datestamp splitsize split_diskbuffer fallback_splitsize
• FILE-WRITE handle filename hostname diskname level datestamp splitsize
• DONE handle (result from dumper send to taper)
• FAILED handle (result from dumper send to taper)
• NEW-TAPE handle
• NO-NEW-TAPE handle
• QUIT

taper reply

• TAPER-OK
• TAPER-ERROR "error-message"
• PARTIAL handle INPUT-* TAPE-* "[sec %f kb %d kps %f]" "input-error-message" "tape-error-message"
  • The statistic are the sum of all successful part (PARTDONE), it should not include the failed part.
• DONE handle INPUT-GOOD TAPE-GOOD "[sec %f kb %d kps %f]" "" ""
  • The statistic are the sum of all successful part (PARTDONE), it should not include the failed part.
• FAILED handle INPUT-* TAPE-* "input-error-message" "tape-error-message"
• NEW-TAPE handle label
• NO-NEW-TAPE handle
• PARTDONE handle label fileno "[sec %f kb %d kps %f]"
• REQUEST-NEW-TAPE handle
• DUMPER-STATUS handle
• QUITTING
• BAD-COMMAND "error message"

LOG

• One PART or PARTPARTIAL log line for all part written to tape. It tell the location and status of each part.
  • PART taper label fileno hostname diskname timestamp part-number/totpart level [sec %f kb %d kps %f]
  • PARTPARTIAL taper label fileno hostname diskname timestamp part-number/totpart level [sec %f kb %d kps %f] "error message"

totpart should be -1 if the the number is not known (PORT-WRITE)

• One DONE/PARTIAL/FAILED for each dump. It tell the status of the complete dump.
  • DONE taper hostname diskname timestamp totpart level [sec %f kb %d kps %f]
    • The statistic is the sum of all successful part (PART), it doesn't include PARTPARTIAL
  • PARTIAL taper hostname diskname timestamp totpart level [sec %f kb %d kps %f] "error message"
    • The statistic is the sum of all successful part (PART), it doesn't include PARTPARTIAL
  • FAILED taper hostname diskname timestamp level "error message"

algorithm after a part written to tape

 if (successful part) {
   L_PART -> logfile
   if (splited dump) {
     PARTDONE -> DRIVER
   if (not splited dump || last part) {
     if (PORT-WRITE) {
       DUMPER-STATUS -> driver
       get dumper result from driver (FAILED|DONE)
     }
     if (partial) #from dumper status or partial flag in header {
       PARTIAL INPUT-GOOD TAPE-GOOD -> driver
       L_PARTIAL -> logfile
     } else (whole) {
       DONE INPUT-GOOD TAPE-GOOD -> driver
       L_SUCCESS -> logfile
     }
   } else #splited dump
     GOTO next part
 } else #failed part {
   if (something written to tape for this part)
     L_PARTPARTIAL -> logfile
   if (splitted dump and tape error && no-input-error) {
     SPLIT_NEEDNEXT -> driver
     L_INFO -> logfile
     #wait for driver NEW-TAPE or NO-NEW-TAPE
     #It could take a long time to get the result
     if(driver sent NEW-TAPE)
       if (new tape available)
         NEW-TAPE -> DRIVER
         GOTO retry that part to the new tape
       else #no valid writable tape found
         NO-NEW-TAPE -> DRIVER
     else #driver sent NO-NEW-TAPE
       noop
   }
   #it's possible to have both INPUT-* and TAPE-* error or none.
   if (nothing written to tape for this dump) {
     FAILED INPUT-* TAPE-*  -> driver
     L_FAIL -> logfile
   } else #something written to tape for this dump {
     PARTIAL INPUT-* TAPE-* -> driver;
     L_PARTIAL -> logfile
   }
 }