-\section*{Migration}
-\label{_MigrationChapter}
+\chapter{Migration}
+\label{MigrationChapter}
\index[general]{Migration}
-\addcontentsline{toc}{section}{Migration}
The term Migration, as used in the context of Bacula, means moving data from
one Volume to another. In particular it refers to a Job (similar to a backup
job) that reads data that was previously backed up to a Volume and writes
-it to another Volume. As part of this process, catalog records associated with the first
-backup job are purged. In other words, Migration moves Bacula Job data from one
-Volume to another. Although we mention Volumes to simplify the subject,
-in reality, Migration is based upon the concept of moving individual Jobs from one Pool to another.
-
-Migrations can be based on quite a number of different criteria such as:
+it to another Volume. As part of this process, the File catalog records
+associated with the first backup job are purged. In other words, Migration
+moves Bacula Job data from one Volume to another by reading the Job data
+from the Volume it is stored on, writing it to a different Volume in a
+different Pool, and then purging the database records for the first Job.
+
+The section process for which Job or Jobs are migrated
+can be based on quite a number of different criteria such as:
\begin{itemize}
\item a single previous Job
\item a Volume
\item a Client
\item a regular expression matching a Job, Volume, or Client name
-\item the time a Job is on a Volume
+\item the time a Job has been on a Volume
\item high and low water marks (usage or occupation) of a Pool
\item Volume size
\end{itemize}
to a Backup Job but with {\bf Type = Migrate} instead of {\bf Type =
Backup}. One of the key points to remember is that the Pool that is
specified for the migration job is the only pool from which jobs will
-be migrated, with one exception noted below.
+be migrated, with one exception noted below. In addition, the Pool to
+which the selected Job or Jobs will be migrated is defined by the {\bf
+Next Pool = ...} in the Pool resource specified for the Migration Job.
+
+Bacula permits pools to contain Volumes with different Media Types.
+However, when doing migration, this is a very undesirable condition. For
+migration to work properly, you should use pools containing only Volumes of
+the same Media Type for all migration jobs.
The migration job normally is either manually started or starts
from a Schedule much like a backup job. It searches
for a previous backup Job or Jobs that match the parameters you have
-specified in the migration Job resource, primiarily a {\bf Selection Type}
+specified in the migration Job resource, primarily a {\bf Selection Type}
(detailed a bit later). Then for
each previous backup JobId found, the Migration Job will run a new Job which
copies the old Job data from the previous Volume to a new Volume in
migration:
\begin{itemize}
-\item The currently running Migration control Job
-\item The previous Backup Job (already run)
+\item The currently running Migration control Job. This is only
+ a control job for starting the migration child jobs.
+\item The previous Backup Job (already run). The File records
+ for this Job are purged if the Migration job successfully
+ terminates. The original data remains on the Volume until
+ it is recycled and rewritten.
\item A new Migration Backup Job that moves the data from the
- previous Backup job to the new Volume.
+ previous Backup job to the new Volume. If you subsequently
+ do a restore, the data will be read from this Job.
\end{itemize}
If the Migration control job finds a number of JobIds to migrate (e.g.
it is asked to migrate one or more Volumes), it will start one new
-migration backup job for each JobId found.
+migration backup job for each JobId found on the specified Volumes.
+Please note that Migration doesn't scale too well since Migrations are
+done on a Job by Job basis. This if you select a very large volume or
+a number of volumes for migration, you may have a large number of
+Jobs that start. Because each job must read the same Volume, they will
+run consecutively (not simultaneously).
-\subsection*{Migration Job Resource Directives}
-\addcontentsline{toc}{section}{Migration Job Resource Directives}
+\section{Migration Job Resource Directives}
The following directives can appear in a Director's Job resource, and they
are used to define a Migration job.
\begin{description}
\item [Pool = \lt{}Pool-name\gt{}] The Pool specified in the Migration
-control Job is not a new directive for the Job resource, but it is
-particularly important because it determines what Pool will be examined for
-finding JobIds to migrate. The exception to this is when {\bf Selection
-Type = SQLQuery}, in which case no Pool is used, unless you
-specifically include it in the SQL query.
+ control Job is not a new directive for the Job resource, but it is
+ particularly important because it determines what Pool will be examined for
+ finding JobIds to migrate. The exception to this is when {\bf Selection
+ Type = SQLQuery}, in which case no Pool is used, unless you
+ specifically include it in the SQL query. Note, the Pool resource
+ referenced must contain a {\bf Next Pool = ...} directive to define
+ the Pool to which the data will be migrated.
\item [Type = Migrate]
-{\bf Migrate} is a new type that defines the job that is run as being a
-Migration Job. A Migration Job is a sort of control job and does not have
-any Files associated with it, and in that sense they are more or less like
-an Admin job. Migration jobs simply check to see if there is anything to Migrate then
-possibly start and control new Backup jobs to migrate the data from the
-specified Pool to another Pool.
+ {\bf Migrate} is a new type that defines the job that is run as being a
+ Migration Job. A Migration Job is a sort of control job and does not have
+ any Files associated with it, and in that sense they are more or less like
+ an Admin job. Migration jobs simply check to see if there is anything to
+ Migrate then possibly start and control new Backup jobs to migrate the data
+ from the specified Pool to another Pool.
\item [Selection Type = \lt{}Selection-type-keyword\gt{}]
The \lt{}Selection-type-keyword\gt{} determines how the migration job
control job will then start and run one migration backup job for
each of the Jobs found on this Volume. The Selection Pattern, if
specified, is not used.
+
\item [OldestVolume] This selection keyword selects the volume with the
oldest last write time in the Pool to be migrated. The Pool to be
migrated is the Pool defined in the Migration Job resource. The
migration control job will then start and run one migration backup
job for each of the Jobs found on this Volume. The Selection
Pattern, if specified, is not used.
+
\item [Client] The Client selection type, first selects all the Clients
that have been backed up in the Pool specified by the Migration
Job resource, then it applies the {\bf Selection Pattern} (defined
filtered (regexed) Clients will be migrated.
The migration control job will then start and run one migration
backup job for each of the JobIds found for those filtered Clients.
+
\item [Volume] The Volume selection type, first selects all the Volumes
that have been backed up in the Pool specified by the Migration
Job resource, then it applies the {\bf Selection Pattern} (defined
filtered (regexed) Volumes will be migrated.
The migration control job will then start and run one migration
backup job for each of the JobIds found on those filtered Volumes.
+
\item [Job] The Job selection type, first selects all the Jobs (as
defined on the {\bf Name} directive in a Job resource)
that have been backed up in the Pool specified by the Migration
Job named, they can be many jobs (JobIds) that ran.
The migration control job will then start and run one migration
backup job for each of the Jobs found.
+
\item [SQLQuery] The SQLQuery selection type, used the {\bf Selection
Pattern} as an SQL query to obtain the JobIds to be migrated.
The Selection Pattern must be a valid SELECT SQL statement for your
SQL engine, and it must return the JobId as the first field
of the SELECT.
- \item [PoolOccupancy] Not yet implemented.
- \item [PoolTime] Not yet implemented.
+
+ \item [PoolOccupancy] This selection type will cause the Migration job
+ to compute the total size of the specified pool for all Media Types
+ combined. If it exceeds the {\bf Migration High Bytes} defined in
+ the Pool, the Migration job will migrate all JobIds beginning with
+ the oldest Volume in the pool (determined by Last Write time) until
+ the Pool bytes drop below the {\bf Migration Low Bytes} defined in the
+ Pool. This calculation should be consider rather approximative because
+ it is made once by the Migration job before migration is begun, and
+ thus does not take into account additional data written into the Pool
+ during the migration. In addition, the calculation of the total Pool
+ byte size is based on the Volume bytes saved in the Volume (Media)
+database
+ entries. The bytes calculate for Migration is based on the value stored
+ in the Job records of the Jobs to be migrated. These do not include the
+ Storage daemon overhead as is in the total Pool size. As a consequence,
+ normally, the migration will migrate more bytes than strictly necessary.
+
+ \item [PoolTime] The PoolTime selection type will cause the Migration job to
+ look at the time each JobId has been in the Pool since the job ended.
+ All Jobs in the Pool longer than the time specified on {\bf Migration Time}
+ directive in the Pool resource will be migrated.
\end{description}
\item [Selection Pattern = \lt{}Quoted-string\gt{}]
\end{description}
-\subsection*{Migration Pool Resource Directives}
-\addcontentsline{toc}{section}{Migration Pool Resource Directives}
+\section{Migration Pool Resource Directives}
The following directives can appear in a Director's Pool resource, and they
-are used to define a Migration job.
+are used to define a Migration job.
\begin{description}
\item [Migration Time = \lt{}time-specification\gt{}]
-If a PoolTime migration is done, the time specified here in seconds (time
-modifiers are permitted -- e.g. hours, ...) will be used. If the
-previous Backup Job or Jobs selected have been in the Pool longer than
-the specified PoolTime, then they will be migrated.
-
+ If a PoolTime migration is done, the time specified here in seconds (time
+ modifiers are permitted -- e.g. hours, ...) will be used. If the
+ previous Backup Job or Jobs selected have been in the Pool longer than
+ the specified PoolTime, then they will be migrated.
+
\item [Migration High Bytes = \lt{}byte-specification\gt{}]
This directive specifies the number of bytes in the Pool which will
trigger a migration if a {\bf PoolOccupancy} migration selection
- type has been specified. Please note, that the fact that the Pool
+ type has been specified. The fact that the Pool
usage goes above this level does not automatically trigger a migration
- job.
+ job. However, if a migration job runs and has the PoolOccupancy selection
+ type set, the Migration High Bytes will be applied. Bacula does not
+ currently restrict a pool to have only a single Media Type, so you
+ must keep in mind that if you mix Media Types in a Pool, the results
+ may not be what you want, as the Pool count of all bytes will be
+ for all Media Types combined.
\item [Migration Low Bytes = \lt{}byte-specification\gt{}]
This directive specifies the number of bytes in the Pool which will
\item [Next Pool = \lt{}pool-specification\gt{}]
The Next Pool directive specifies the pool to which Jobs will be
- migrated.
+ migrated. This directive is required to define the Pool into which
+ the data will be migrated. Without this directive, the migration job
+ will terminate in error.
\item [Storage = \lt{}storage-specification\gt{}]
The Storage directive specifies what Storage resource will be used
for all Jobs that use this Pool. It takes precedence over any other
Storage specifications that may have been given such as in the
- Schedule Run directive, or in the Job resource.
-
+ Schedule Run directive, or in the Job resource. We highly recommend
+ that you define the Storage resource to be used in the Pool rather
+ than elsewhere (job, schedule run, ...).
\end{description}
-\subsection*{Example Migration Jobs}
+\section{Important Migration Considerations}
+\index[general]{Important Migration Considerations}
+\begin{itemize}
+\item Each Pool into which you migrate Jobs or Volumes {\bf must}
+ contain Volumes of only one Media Type.
+
+\item Migration takes place on a JobId by JobId basis. That is
+ each JobId is migrated in its entirety and independently
+ of other JobIds. Once the Job is migrated, it will be
+ on the new medium in the new Pool, but for the most part,
+ aside from having a new JobId, it will appear with all the
+ same characteristics of the original job (start, end time, ...).
+ The column RealEndTime in the catalog Job table will contain the
+ time and date that the Migration terminated, and by comparing
+ it with the EndTime column you can tell whether or not the
+ job was migrated. The original job is purged of its File
+ records, and its Type field is changed from "B" to "M" to
+ indicate that the job was migrated.
+
+\item Jobs on Volumes will be Migration only if the Volume is
+ marked, Full, Used, or Error. Volumes that are still
+ marked Append will not be considered for migration. This
+ prevents Bacula from attempting to read the Volume at
+ the same time it is writing it. It also reduces other deadlock
+ situations, as well as avoids the problem that you migrate a
+ Volume and later find new files appended to that Volume.
+
+\item As noted above, for the Migration High Bytes, the calculation
+ of the bytes to migrate is somewhat approximate.
+
+\item If you keep Volumes of different Media Types in the same Pool,
+ it is not clear how well migration will work. We recommend only
+ one Media Type per pool.
+
+\item It is possible to get into a resource deadlock where Bacula does
+ not find enough drives to simultaneously read and write all the
+ Volumes needed to do Migrations. For the moment, you must take
+ care as all the resource deadlock algorithms are not yet implemented.
+
+\item Migration is done only when you run a Migration job. If you set a
+ Migration High Bytes and that number of bytes is exceeded in the Pool
+ no migration job will automatically start. You must schedule the
+ migration jobs, and they must run for any migration to take place.
+
+\item If you migrate a number of Volumes, a very large number of Migration
+ jobs may start.
+
+\item Figuring out what jobs will actually be migrated can be a bit complicated
+ due to the flexibility provided by the regex patterns and the number of
+ different options. Turning on a debug level of 100 or more will provide
+ a limited amount of debug information about the migration selection
+ process.
+
+\item Bacula currently does only minimal Storage conflict resolution, so you
+ must take care to ensure that you don't try to read and write to the
+ same device or Bacula may block waiting to reserve a drive that it
+ will never find. In general, ensure that all your migration
+ pools contain only one Media Type, and that you always
+ migrate to pools with different Media Types.
+
+\item The {\bf Next Pool = ...} directive must be defined in the Pool
+ referenced in the Migration Job to define the Pool into which the
+ data will be migrated.
+
+\item Pay particular attention to the fact that data is migrated on a Job
+ by Job basis, and for any particular Volume, only one Job can read
+ that Volume at a time (no simultaneous read), so migration jobs that
+ all reference the same Volume will run sequentially. This can be a
+ potential bottle neck and does not scale very well to large numbers
+ of jobs.
+
+\item Only migration of Selection Types of Job and Volume have
+ been carefully tested. All the other migration methods (time,
+ occupancy, smallest, oldest, ...) need additional testing.
+
+\item Migration is only implemented for a single Storage daemon. You
+ cannot read on one Storage daemon and write on another.
+\end{itemize}
+
+
+\section{Example Migration Jobs}
\index[general]{Example Migration Jobs}
-\addcontentsline{toc}{subsection}{Example Migration Jobs}
+
+When you specify a Migration Job, you must specify all the standard
+directives as for a Job. However, certain such as the Level, Client, and
+FileSet, though they must be defined, are ignored by the Migration job
+because the values from the original job used instead.
As an example, suppose you have the following Job that
-you run every night:
+you run every night. To note: there is no Storage directive in the
+Job resource; there is a Storage directive in each of the Pool
+resources; the Pool to be migrated (File) contains a Next Pool
+directive that defines the output Pool (where the data is written
+by the migration job).
\footnotesize
\begin{verbatim}
\normalsize
Where we have included only the essential information -- i.e. the
-Director, FileSet, Catalog, Client, Schedule, and Messages resources are omitted.
+Director, FileSet, Catalog, Client, Schedule, and Messages resources are
+omitted.
As you can see, by running the NightlySave Job, the data will be backed up
to File storage using the Default pool to specify the Storage as File.
Client = rufus-fd
FileSet = "Full Set"
Messages = Standard
- Storage = DLTDrive
Pool = Default
Maximum Concurrent Jobs = 4
Selection Type = Volume
Client = rufus-fd
FileSet="Full Set"
Messages = Standard
- Storage = DLTDrive
Pool = Default
Maximum Concurrent Jobs = 4
Selection Type = Job
projects / bacula / docs / blobdiff