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<LI><A NAME="tex2html864"
HREF="Save_Protocol_Between_File.html#SECTION00661000000000000000">Command and Control Information</A>
<LI><A NAME="tex2html865"
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<H1><A NAME="SECTION00660000000000000000"></A>
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The Save Protocol Between the File Daemon and the Storage Daemon
</H1>
<P>
Once the Director has send a <B>save</B> command to the File daemon, the File
daemon will contact the Storage daemon to begin the save.
<P>
In what follows: FD: refers to information set via the network from the File
daemon to the Storage daemon, and SD: refers to information set from the
Storage daemon to the File daemon.
<P>
<H2><A NAME="SECTION00661000000000000000"></A>
<A NAME="1879"></A>
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Command and Control Information
</H2>
<P>
Command and control information is exchanged in human readable ASCII commands.
<P>
<PRE>
FD: listens
SD: makes connection
FD: append open session = <JobId> [<password>]
SD: 3000 OK ticket = <number>
FD: append data <ticket-number>
SD: 3000 OK data address = <IPaddress> port = <port>
</PRE>
<P>
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<BR>
Data Information
</H2>
<P>
The Data information consists of the file attributes and data to the Storage
daemon. For the most part, the data information is sent one way: from the File
daemon to the Storage daemon. This allows the File daemon to transfer
information as fast as possible without a lot of handshaking and network
overhead.
<P>
However, from time to time, the File daemon needs to do a sort of checkpoint
of the situation to ensure that everything is going well with the Storage
daemon. To do so, the File daemon sends a packet with a negative length
indicating that he wishes the Storage daemon to respond by sending a packet of
information to the File daemon. The File daemon then waits to receive a packet
from the Storage daemon before continuing.
<P>
All data sent are in binary format except for the header packet, which is in
ASCII. There are two packet types used data transfer mode: a header packet,
the contents of which are known to the Storage daemon, and a data packet, the
contents of which are never examined by the Storage daemon.
<P>
The first data packet to the Storage daemon will be an ASCII header packet
consisting of the following data.
<P>
File-Index Stream-Id Info where <B>File-Index</B> is a sequential number beginning from one that
increments with each file (or directory) sent.
<P>
where <B>Stream-Id</B> will be 1 for the Attributes record and 2 for
uncompressed File data. 3 is reserved for the MD5 signature for the file.
<P>
where <B>Info</B> transmit information about the Stream to the
Storage Daemon. It is a character string field where each character has a
meaning. The only character currently defined is 0 (zero), which is simply a
place holder (a no op). In the future, there may be codes indicating
compressed data, encrypted data, etc.
<P>
Immediately following the header packet, the Storage daemon will expect any
number of data packets. The series of data packets is terminated by a zero
length packet, which indicates to the Storage daemon that the next packet will
be another header packet. As previously mentioned, a negative length packet is
a request for the Storage daemon to temporarily enter command mode and send a
reply to the File daemon. Thus an actual conversation might contain the
following exchanges:
<P>
<PRE>
FD: <1 1 0> (header packet)
FD: <data packet containing file-attributes>
FD: Null packet
FD: <1 2 0>
FD: <multiple data packets containing the file data>
FD: Packet length = -1
SD: 3000 OK
FD: <2 1 0>
FD: <data packet containing file-attributes>
FD: Null packet
FD: <2 2 0>
FD: <multiple data packets containing the file data>
FD: Null packet
FD: Null packet
FD: append end session <ticket-number>
SD: 3000 OK end
FD: append close session <ticket-number>
SD: 3000 OK Volumes = <number of volumes>
SD: 3001 Volume = <volumeid> <start file> <start block>
<end file> <end block> <volume session-id>
SD: 3002 Volume data = <date/time of last write> <Number bytes written>
<number errors>
SD: ... additional Volume / Volume data pairs for
volumes 2 .. n
FD: close socket
</PRE>
<P>
The information returned to the File daemon by the Storage daemon in response
to the <B>append close session</B> is transmit in turn to the Director.
<P>
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2012-01-24
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