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- Chapter 24. Amanda Internals
-Prev Part V. Technical Background Next
-
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-
-Chapter 24. Amanda Internals
-
-
-George Scott
-
-Original text<George.Scott@cc.monash.edu.au>
-
-Stefan G. Weichinger
-
-XML-conversion
-AMANDA Core Team
-<sgw@amanda.org>
-Table of Contents
-
-
- Protocols
-
- server_and_amandad_on_client
-
- planner_and_driver
-
- driver_and_dumper
-
- taper(read)_and_taper(write)
-
-This is an attempt to document Amanda's internals. Please feel free to make
-comments and suggest changes. Text for new sections gratefully accepted!
-
- Protocols
-
-
-Note
-
-The following was an ASCII-illustration in the original docs, I managed to
-transfer it at last. Maybe someone will convert this to the first image in the
-Amanda-docs ;-) . sgw.
-
-
- Client I Server +-planner-+
- I | |
- I | |
- I | | ______
- +-amandad-+ I | | (______)
- | | I | | |amdump|
- | | I | | all ::::>| |
- | | I | | stderr | |
- | | I | | | |
- | | I | so | +------+
- | | I +---------+
- | | I :: ______
- | | I \/ (______)
- | | I +-driver--+ | log |
- +---------+ I | si | all ::::>| |
- I | | log | |
- I | | | |
- +-sendback+ I | | +------+
- | | I | |
- | | I ::::::::| |<::::::
- | | I :: | | ::
- | | I :: ::::>| |:::: ::
- | | I :: :: | | :: ::
- | | I :: :: +---------+ :: ::
- | | I :: :: :: ::
- | | I :: :: :: ::
- | | I :: :: ______ :: ::
- +---------+ I :: :: (______) :: ::
- I :: :: | /tmp | :: ::
- I \/ :: :>| | \/ ::
- +-dump----+ I +-dumper--+ :: +------+ +-taper/r-+ +-taper/w-+
- | | I | si so | :: | si so | | |
- | | I | | :: ______ | | | |
- | | I |mesgfd | :: (______) | | | |
- | se|::::>|::::::::>|:: | hold | | | | |
- | | I | errf| | disk | | p2c|:::>|p2c |
- | | I | | | | | c2p|<:::|c2p |
- ____
- | | I |datafd | ::>| |::: |fd | | | / \
- | so|::::>|::::::::>|:: +------+ :>|::::::::>SHDMEM::::::::>|::
- >|tape|
- | | I | outfd| :: :: | | | tapefd| \ _ /
- +---------+ I +---------+ :::::::::::: +---------+ +---------+
- I
-
-
- server and amandad on client
-
-XXX - still to be done
-
- planner and driver
-
-planner interrogates all clients and generates a plan of which disks to backup
-and what dump level to do them at. The plan is plain text with one line per
-disk to be dumped. It is piped from planners stdout to drivers stdin. Plan
-lines come in two flavours:
-For total dumps: <host> <disk> <pri> <lev> <size> <time> <deg lev> <deg size>
-<deg time>
-For incremental dumps: <host> <disk> <pri> <lev> <size> <time>
-Where: <host> Host name of client (from disklist file) <disk> Name of disk
-(from disklist file) <pri> Priority of backup (pri from disklist and
-amanda.conf + days overdue for total) <lev> Dump level for dump (0 for total,
-1-9 for incremental) <size> Estimated size (in Kb after compression if
-requested) <time> Estimated time for backup (in seconds) <deg lev> <lev> to use
-if in degraded mode <deg size> <size> to use if in degraded mode <deg time>
-<time> to use if in degraded mode
-
- driver and dumper
-
-dumper talks via two pipes connected to each dumper's stdin and stdout. The
-commands and responses are plain text.
-driver can ask dumper to do a dump to a file on the holding disk: FILE-DUMP
-<handle> <filename> <host> <disk> <level> <dumpdate> <chunksize> <prog>
-<options> or directly to taper: PORT-DUMP <handle> <port> <host> <disk> <level>
-<dumpdate> <prog> <options> or exit at the end of the run: QUIT
-If the dump finishes correctly dumper replies with: DONE <handle> [<message>]
-If something goes wrong with the dump, dumper can request that the dump be
-retried at a later time with: TRY-AGAIN <handle> [<message>] or, for fatal
-errors, be abandoned with: FAILED <handle> [<message>]
-If the holding disk runs out of space, dumper will give: NO-ROOM <handle> and
-wait for driver to either fix the problem and say: CONTINUE or just say: ABORT
-in which case dumper kills the dump and replies with: ABORT-FINISHED <handle>
-If driver says something that dumper doesn't recognise it responds with: BAD-
-COMMAND <message>
-Where: <handle> Request ID <filename> Name of file (on holding disk) to write
-dump <port> Port (of taper) to send dump directly <host> Hostname of client
-<disk> Disk to backup <level> Dump level to do backup at <prog> Dump program to
-use <options> Options to pass to sendbackup <message> Error or status message
-*driver and taper
-driver talks via two pipes connected to taper's stdin and stdout. The commands
-and responses are plain text.
-driver initialises taper with: START-TAPER <datestamp> to which taper replies
-with: TAPER-OK or, for fatal errors, with: TAPER-ERROR [<message>]
-driver can ask taper to to copy a file from the holding disk to tape: FILE-
-WRITE <handle> <filename> <host> <disk> <level> or directly from a dumper:
-PORT-WRITE <handle> <host> <disk> <level> 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.
-taper responds to the QUIT command with: QUITING
-If the copy to tape finishes correctly taper replies with: DONE <handle>
-[<message>]
-If something goes wrong with the tape, taper can request that the dump be
-retried at a later time with: TRY-AGAIN <handle> [<message>] or, for fatal
-errors, be abandoned with: TAPE-ERROR <handle> [<message>]
-If driver says something that taper doesn't recognise it responds with: BAD-
-COMMAND <message>
-Where: <datestamp> Todays date as "yymmdd" <handle> Request ID <filename> Name
-of file (on holding disk) to write dump <port> Port (of taper) to send dump
-directly <host> Hostname of client <disk> Disk to backup <level> Dump level to
-do backup at <message> Error or status message
-
- taper(read) and taper(write)
-
-There are two parts to taper: the file reader and the tape writer.
-Communication between the two sides is via a bit of shared memory for data
-transfer and two pipes (one in each direction) for synchronisation.
-The shared memory area is made up of NBUFS (=20) buffers each of which contains
-a status word and a BUFFER_SIZE (=32*1024) byte data buffer.
-The sync pipes are used to transfer a simplistic command sequence:
-reader writer ------ ------
-Startup S<datestamp> ---> <--- S Start OK <--- E<messge> Error
-Open tape O<datestamp><hostname><diskname><level> ---> <--- O Opening
-Write buffer W<bufnum> ---> <--- R<bufnum> Buffer empty <--- E<message> Error
-<--- T<message> Error, try again E ack e ---> Protocol error X ---> <--- x X
-ack
-Close tape C ---> <--- C<label><filenum><stats> Closing
-Quit Q --->
-
-Note
-
-Refer to http://www.amanda.org/docs/internals.html for the current version of
-this document.
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