1%%
2%%
3
4\chapter{Data Spooling}
5\label{SpoolingChapter}
6\index[general]{Data Spooling }
7\index[general]{Spooling!Data }
8
9Bacula allows you to specify that you want the Storage daemon to initially
10write your data to disk and then subsequently to tape. This serves several
11important purposes.
12
13\begin{itemize}
14\item It takes a long time for data to come in from the File daemon during
15   an Incremental backup.  If it is directly written to tape, the tape will
16   start and stop or shoe-shine as it is often called causing tape wear.
17   By first writing the data to disk, then writing it to tape, the tape can
18   be kept in continual motion.
19\item While the spooled data is being written to the tape, the despooling
20   process has exclusive use of the tape.  This means that you can spool
21   multiple simultaneous jobs to disk, then have them very efficiently
22   despooled one at a time without having the data blocks from several jobs
23   intermingled, thus substantially improving the time needed to restore
24   files. While despooling, all jobs spooling continue running.
25\item Writing to a tape can be slow.  By first spooling your data to disk,
26   you can often reduce the time the File daemon is running on a system,
27   thus reducing downtime, and/or interference with users.  Of course, if
28   your spool device is not large enough to hold all the data from your
29   File daemon, you may actually slow down the overall backup.
30\end{itemize}
31
32Data spooling is exactly that "spooling".  It is not a way to first write a
33"backup" to a disk file and then to a tape.  When the backup has only been
34spooled to disk, it is not complete yet and cannot be restored until it is
35written to tape.
36
37Bacula version 1.39.x and later supports writing a backup
38to disk then later {\bf Migrating} or moving it to a tape (or any
39other medium). For
40details on this, please see the \ilink{Migration}{MigrationChapter} chapter
41of this manual for more details.
42
43The remainder of this chapter explains the various directives that you can use
44in the spooling process.
45
46\label{directives}
47\section{Data Spooling Directives}
48\index[general]{Directives!Data Spooling }
49\index[general]{Data Spooling Directives }
50
51The following directives can be used to control data spooling.
52
53\begin{itemize}
54\item To turn data spooling on/off at the Job level in  the Job resource in
55   the Director's conf file (default  {\bf no}).
56
57{\bf SpoolData = yes\vb{}no}
58
59\item To override the Job specification in a Schedule Run  directive in the
60   Director's conf file.
61
62{\bf SpoolData = yes\vb{}no}
63
64\item To override the Job specification in a bconsole session using the \texttt{run}
65   command. Please note that this does {\bf not } refer to a configuration
66   statement, but to an argument for the run command.
67
68{\bf SpoolData=yes\vb{}no}
69
70\item To limit the the maximum spool file size for a particular job in the Job
71  resource
72
73{\bf Spool Size = size}
74   Where size is a the maximum spool size for this job  specified in bytes.
75
76\item To limit the maximum total size of the spooled data  for a particular
77   device. Specified in the Device  resource of the Storage daemon's conf file
78   (default  unlimited).
79
80{\bf Maximum Spool Size = size}
81   Where size is a the maximum spool size for all jobs  specified in bytes.
82
83\item To limit the maximum total size of the spooled data  for a particular
84   device for a single job. Specified  in the Device Resource of the Storage
85   daemon's conf  file (default unlimited).
86
87{\bf Maximum Job Spool Size = size}
88   Where size is the maximum spool file size for a single  job specified in
89   bytes.
90
91\item To specify the spool directory for a particular device.  Specified in
92   the Device Resource of the Storage daemon's conf  file (default, the working
93   directory).
94
95{\bf Spool Directory = directory}
96\end{itemize}
97
98\label{warning}
99
100% TODO: fix this section name
101\section{!!! MAJOR WARNING !!!}
102\index[general]{WARNING! MAJOR }
103\index[general]{ MAJOR WARNING  }
104
105Please be very careful to exclude the spool directory from any backup,
106otherwise, your job will write enormous amounts of data to the Volume, and
107most probably terminate in error. This is because in attempting to backup the
108spool file, the backup data will be written a second time to the spool file,
109and so on ad infinitum.
110
111Another advice is to always specify the maximum spool size so that your disk
112doesn't completely fill up. In principle, data spooling will properly detect a
113full disk, and despool data allowing the job to continue. However, attribute
114spooling is not so kind to the user. If the disk on which attributes are being
115spooled fills, the job will be canceled. In addition, if your working
116directory is on the same partition as the spool directory, then Bacula jobs
117will fail possibly in bizarre ways when the spool fills.
118
119\label{points}
120\section{Other Points}
121\index[general]{Points!Other }
122\index[general]{Other Points }
123
124\begin{itemize}
125\item When data spooling is enabled, Bacula automatically  turns on attribute
126   spooling. In other words, it also  spools the catalog entries to disk. This is
127   done so  that in case the job fails, there will be no catalog  entries
128   pointing to non-existent tape backups.
129\item Attribute despooling occurs near the end of a job.  The Storage daemon
130   accumulates file attributes during the backup and  sends them to the
131   Director at the end of the job.  The Director then inserts the file
132   attributes into the catalog.  During this insertion, the tape drive may
133   be inactive.  When the file attribute insertion is completed, the job
134   terminates.
135\item Attribute spool files are always placed in the  working directory of
136   the Storage daemon.
137\item When Bacula begins despooling data spooled to disk, it  takes exclusive
138   use of the tape. This has the major  advantage that in running multiple
139   simultaneous jobs at  the same time, the blocks of several jobs will not be
140   intermingled.
141\item It probably does not make a lot of sense to enable data  spooling if you
142   are writing to disk files.
143\item It is probably best to provide as large a spool file as  possible to
144   avoid repeatedly spooling/despooling. Also,  while a job is despooling to
145   tape, the File daemon must wait  (i.e. spooling stops for the job while it is
146   despooling).
147\item If you are running multiple simultaneous jobs, Bacula  will continue
148   spooling other jobs while one is despooling  to tape, provided there is
149   sufficient spool file space.
150\end{itemize}
151