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[bacula/docs] / docs / manual-fr / recycling.tex

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\section*{Automatic Volume Recycling}
\label{_ChapterStart22}
\index[general]{Recycling!Automatic Volume }
\index[general]{Automatic Volume Recycling }
\addcontentsline{toc}{section}{Automatic Volume Recycling}

Normally, Bacula will write on a volume, and once the tape is written, it can
append to the volume, but it will never overwrite the data thus destroying it.
When we speak of {\bf recycling} volumes, we mean that {\bf Bacula} can write
over the previous contents of a volume. Thus all previous data will be lost. 

You may not want Bacula to automatically recycle (reuse) tapes. This requires
a large number of tapes, and in such a case, it is possible to manually
recycle tapes. For more on manual recycling, see the section entitled 
\ilink{ Manually Recycling Volumes}{manualrecycling} below in
this chapter. 

Most people prefer to have a Pool of tapes that are used for daily backups and
recycled once a week, another Pool of tapes that are used for Full backups
once a week and recycled monthly, and finally a Pool of tapes that are used
once a month and recycled after a year or two. With a scheme like this, your
pool of tapes remains constant. 

By properly defining your Volume Pools with appropriate Retention periods,
Bacula can manage the recycling (such as defined above) automatically. 

Automatic recycling of Volumes is controlled by three records in the {\bf
Pool} resource definition in the Director's configuration file. These three
records are: {\bf 

\begin{itemize}
\item AutoPrune = yes 
\item VolumeRetention = \lt{}time\gt{} 
\item Recycle = yes 
   \end{itemize}

} Automatic recycling of Volumes is performed by Bacula only when it wants a
new Volume and no appendable Volumes are available in the Pool. It will then
search the Pool for any Volumes with the {\bf Recycle} flag set and whose
Volume Status is {\bf Full}. At that point, the recycling occurs in two steps.
The first is that the Catalog for a Volume must be purged of all Jobs and
Files contained on that Volume, and the second step is the actual recycling of
the Volume. The Volume will be purged if the VolumeRetention period has
expired. When a Volume is marked as Purged, it means that no Catalog records
reference that Volume, and the Volume can be recycled. Until recycling
actually occurs, the Volume data remains intact. If no Volumes can be found
for recycline for any of the reasons stated above, Bacula will request
operator intervention (i.e. it will ask you to label a new volume). 

A key point mentioned above that can be a source of frustration is that Bacula
will only recycle purged Volumes if there is no other appendable Volume
available, otherwise, it will always write to an appendable Volume before
recycling even if there are Volume marked as Purged. This preserves your data
as long as possible. So, if you wish to ``force'' Bacula to use a purged
Volume, you must first ensure that no other Volume in the Pool is marked {\bf
Append}. If necessary, you can manually set a volume to {\bf Full}. The reason
for this is that Bacula wants to preserve the data on your old tapes (even
though purged from the catalog) as long as absolutely possible before
overwriting it. 
\label{AutoPruning}

\subsection*{Automatic Pruning}
\index[general]{Automatic Pruning }
\index[general]{Pruning!Automatic }
\addcontentsline{toc}{subsection}{Automatic Pruning}

As Bacula writes files to tape, it keeps a list of files, jobs, and volumes in
a database called the catalog. Among other things, the database helps Bacula
to decide which files to back up in an incremental or differential backup, and
helps you locate files on past backups when you want to restore something.
However, the catalog will grow larger and larger as time goes on, and
eventually it can become unacceptably large. 

Bacula's process for removing entries from the catalog is called Pruning. The
default is Automatic Pruning, which means that once an entry reaches a certain
age (e.g. 30 days old) it is removed from the catalog. Once a job has been
pruned, you can still restore it from the backup tape, but one additional step
is required: scanning the volume with bscan. The alternative to Automatic
Pruning is Manual Pruning, in which you explicitly tell Bacula to erase the
catalog entries for a volume. You'd usually do this when you want to reuse a
Bacula volume, because there's no point in keeping a list of files that USED
TO BE on a tape. Or, if the catalog is starting to get too big, you could
prune the oldest jobs to save space. Manual pruning is done with the 
\ilink{ prune command}{ManualPruning} in the console. (thanks to
Bryce Denney for the above explanation). 

\subsection*{Prunning Directives}
\index[general]{Prunning Directives }
\index[general]{Directives!Prunning }
\addcontentsline{toc}{subsection}{Prunning Directives}

There are three pruning durations. All apply to catalog database records and
not to the actual data in a Volume. The pruning (or retention) durations are
for: Volumes (Media records), Jobs (Job records), and Files (File records).
The durations inter-depend a bit because if Bacula prunes a Volume, it
automatically removes all the Job records, and all the File records. Also when
a Job record is pruned, all the File records for that Job are also pruned
(deleted) from the catalog. 

Having the File records in the database means that you can examine all the
files backed up for a particular Job. They take the most space in the catalog
(probably 90-95\% of the total). When the File records are pruned, the Job
records can remain, and you can still examine what Jobs ran, but not the
details of the Files backed up. In addition, without the File records, you
cannot use the Console restore command to restore the files. 

When a Job record is pruned, the Volume (Media record) for that Job can still
remain in the database, and if you do a ``list volumes'', you will see the
volume information, but the Job records (and its File records) will no longer
be available. 

In each case, pruning removes information about where older files are, but it
also prevents the catalog from growing to be too large. You choose the
retention periods in function of how many files you are backing up and the
time periods you want to keep those records online, and the size of the
database.You can always re-insert the records (with 98\% of the original data)
by using ``bscan'' to scan in a whole Volume or any part of the volume that
you want. 

By setting {\bf AutoPrune} to {\bf yes} you will permit {\bf Bacula} to
automatically prune all Volumes in the Pool when a Job needs another Volume.
Volume pruning means removing records from the catalog. It does not shrink the
size of the Volume or effect the Volume data until the Volume gets
overwritten. When a Job requests another volume and there are no Volumes with
Volume Status {\bf Append} available, Bacula will begin volume pruning. This
means that all Jobs that are older than the {\bf VolumeRetention} period will
be pruned from every Volume that has Volume Status {\bf Full} or {\bf Used}
and has Recycle set to {\bf yes}. Pruning consists of deleting the
corresponding Job, File, and JobMedia records from the catalog database. No
change to the physical data on the Volume occurs during the pruning process.
When all files are pruned from a Volume (i.e. no records in the catalog), the
Volume will be marked as {\bf Purged} implying that no Jobs remain on the
volume. The Pool records that control the pruning are described below. 

\begin{description}

\item [AutoPrune = \lt{}yes|no\gt{}]
   \index[console]{AutoPrune  }
   If AutoPrune is set to  {\bf yes} (default), Bacula (version 1.20 or greater)
will  automatically apply the Volume retention period when running a Job  and
it needs a new Volume but no appendable volumes are available.  At that point,
Bacula will prune all Volumes that can be pruned  (i.e. AutoPrune set) in an
attempt to find a usable volume. If  during the autoprune, all files are
pruned from the Volume, it  will be marked with VolStatus {\bf Purged}.  The
default is {\bf yes}.  

\item [Volume Retention = \lt{}time-period-specification\gt{}]
   \index[console]{Volume Retention  }
   The  Volume Retention record defines the length of time that  Bacula will
guarantee that the Volume is not reused counting  from the time the last job
stored on the Volume terminated.  

When this time period expires, and if {\bf AutoPrune} is set to  {\bf yes},
and a new Volume is needed, but no appendable Volume  is available, Bacula
will prune (remove) Job records that  are older than the specified Volume
Retention period.  

The Volume Retention period takes precedence  over any Job Retention period
you have specified in the  Client resource. It should also be noted, that the
Volume  Retention period is obtained by reading the Catalog Database Media 
record rather than the Pool resource record. This means that  if you change
the VolumeRetention in the Pool resource record,  you must ensure that the
corresponding change is made in the  catalog by using the {\bf update pool}
command. Doing so  will insure that any new Volumes will be created with the 
changed Volume Retention period. Any existing Volumes will  have their own
copy of the Volume Retention period that can  only be changed on a Volume by
Volume basis using the  {\bf update volume} command.  

When all file catalog entries are removed from the volume,  its VolStatus is
set to {\bf Purged}. The files remain physically  on the Volume until the
volume is overwritten.  

Retention periods are specified in seconds,  minutes, hours, days, weeks,
months,  quarters, or years on the record. See the  
\ilink{Configuration chapter}{Time} of this  manual for
additional details of time specification.  

The default is 1 year. 

\item [Recycle = \lt{}yes|no\gt{}]
   \index[fd]{Recycle  }
   This statement tells Bacula  whether or not the particular Volume can be
recycled (i.e.  rewritten). If Recycle is set to {\bf no}  (the default), then
even if Bacula prunes all the Jobs  on the volume and it is marked {\bf
Purged}, it will not  consider the tape for recycling. If Recycle is set to
{\bf yes}  and all Jobs have been pruned, the volume status will be set to 
{\bf Purged} and the volume may then be reused when another  volume is needed.
If the volume is reused, it is relabeled with  the same Volume Name, however
all previous data will be lost. 
\end{description}

Note, it is also possible to ``force'' pruning of all Volumes in the Pool
associated with a Job by adding {\bf Prune Files = yes} to the Job resource. 
\label{Recycling}

\subsection*{Recycling Algorithm}
\index[general]{Algorithm!Recycling }
\index[general]{Recycling Algorithm }
\addcontentsline{toc}{subsection}{Recycling Algorithm}

After all Volumes of a Pool have been pruned (as mentioned above, this happens
when a Job needs a new Volume and no appendable Volumes are available), Bacula
will look for the oldest Volume that is Purged (all Jobs and Files expired),
and if the {\bf Recycle} flag is on (Recycle=yes) for that Volume, Bacula will
relabel it and write new data on it. 

The full recycling algorithm that Bacula uses when it needs a new Volume is: 

\begin{itemize}
\item Search the Pool for a Volume with VolStatus=Append (if there is  more
   than one, the Volume with the oldest date last written is  chosen. If two have
   the same date then the one with  the lowest MediaId is chosen). 
\item Search the Pool for a Volume with VolStatus=Recycle (if there is  more
   than one, the Volume with the oldest date last written is  chosen. If two have
   the same date then the one with  the lowest MediaId is chosen). 
\item Prune volumes applying Volume retention period (Volumes with VolStatus 
   Full, Used, or Append are pruned). 
\item Search the Pool for a Volume with VolStatus=Purged 
\item Attempt to create a new Volume if automatic labeling enabled 
\item Prune the oldest Volume if RecycleOldestVolume=yes (the Volume  with the
   oldest LastWritten date and VolStatus equal to  Full, Recycle, Purged, Used,
   or Append is chosen). This  record ensures that all retention periods are
properly  respected. 
\item Purge the oldest Volume if PurgeOldestVolume=yes (the Volume  with the
   oldest LastWritten date and VolStatus equal to  Full, Recycle, Purged, Used,
   or Append is chosen). We strongly  recommend against the use of {\bf
PurgeOldestVolume} as it  can quite easily lead to loss of current backup
data. 
\item Give up and ask operator. 
   \end{itemize}

The above occurs when Bacula has finished writing a Volume or when no Volume
is present in the drive. 

On the other hand, if you have inserted a different Volume after the last job,
and Bacula recognizes the Volume as valid, it will request authorization from
the Director to use this Volume. In this case, if you have set {\bf Recycle
Current Volume = yes} and the Volume is marked as Used or Full, Bacula will
prune the volume and if all jobs were removed during the pruning (respecting
the retention periods), the Volume will be recycled and used. For this to
work, you must have {\bf Accept Any Volume = yes} in the Pool. The recycling
algorithm in this case is: 

\begin{itemize}
\item If the VolStatus is {\bf Append} or {\bf Recycle}  and {\bf Accept Any
   Volume} is set, the volume  will be used.  
\item If {\bf Recycle Current Volume} is set and the  volume is marked {\bf
   Full} or {\bf Used}, Bacula  will prune the volume (applying the retention
   period).  If all Jobs are pruned from the volume, it will be  recycled. 
\end{itemize}

This permits users to manually change the Volume every day and load tapes in
an order different from what is in the catalog, and if the volume does not
contain a current copy of your backup data, it will be used. 

\subsection*{Recycle Status}
\index[general]{Status!Recycle }
\index[general]{Recycle Status }
\addcontentsline{toc}{subsection}{Recycle Status}

Each Volume inherits the Recycle status (yes or no) from the Pool resource
record when the Media record is created (normally when the Volume is labeled).
This Recycle status is stored in the Media record of the Catalog. Using the
the Console program, you may subsequently change the Recycle status for each
Volume. For example in the following output from {\bf list volumes}: 

\footnotesize
\begin{verbatim}
+----------+-------+--------+---------+------------+--------+-----+
| VolumeNa | Media | VolSta | VolByte | LastWritte | VolRet | Rec |
+----------+-------+--------+---------+------------+--------+-----+
| File0001 | File  | Full   | 4190055 | 2002-05-25 | 14400  | 1   |
| File0002 | File  | Full   | 1896460 | 2002-05-26 | 14400  | 1   |
| File0003 | File  | Full   | 1896460 | 2002-05-26 | 14400  | 1   |
| File0004 | File  | Full   | 1896460 | 2002-05-26 | 14400  | 1   |
| File0005 | File  | Full   | 1896460 | 2002-05-26 | 14400  | 1   |
| File0006 | File  | Full   | 1896460 | 2002-05-26 | 14400  | 1   |
| File0007 | File  | Purged | 1896466 | 2002-05-26 | 14400  | 1   |
+----------+-------+--------+---------+------------+--------+-----+
\end{verbatim}
\normalsize

all the volumes are marked as recyclable, and the last Volume, {\bf File0007}
has been purged, so it may be immediately recycled. The other volumes are all
marked recyclable and when their Volume Retention period (14400 seconds or 4
hours) expires, they will be eligible for pruning, and possible recycling.
Even though Volume {\bf File0007} has been purged, all the data on the Volume
is still recoverable. A purged Volume simply means that there are no entries
in the Catalog. Even if the Volume Status is changed to {\bf Recycle}, the
data on the Volume will be recoverable. The data is lost only when the Volume
is re-labeled and re-written. 

To modify Volume {\bf File0001} so that it cannot be recycled, you use the
{\bf update volume pool=File} command in the console program, or simply {\bf
update} and Bacula will prompt you for the information. 

\footnotesize
\begin{verbatim}
+----------+------+-------+---------+-------------+-------+-----+
| VolumeNa | Media| VolSta| VolByte | LastWritten | VolRet| Rec |
+----------+------+-------+---------+-------------+-------+-----+
| File0001 | File | Full  | 4190055 | 2002-05-25  | 14400 | 0   |
| File0002 | File | Full  | 1897236 | 2002-05-26  | 14400 | 1   |
| File0003 | File | Full  | 1896460 | 2002-05-26  | 14400 | 1   |
| File0004 | File | Full  | 1896460 | 2002-05-26  | 14400 | 1   |
| File0005 | File | Full  | 1896460 | 2002-05-26  | 14400 | 1   |
| File0006 | File | Full  | 1896460 | 2002-05-26  | 14400 | 1   |
| File0007 | File | Purged| 1896466 | 2002-05-26  | 14400 | 1   |
+----------+------+-------+---------+-------------+-------+-----+
\end{verbatim}
\normalsize

In this case, {\bf File0001} will never be automatically recycled. The same
effect can be achieved by setting the Volume Status to Read-Only. 

\subsection*{Making Bacula Use a Single Tape}
\label{singletape}
\index[general]{Tape!Making Bacula Use a Single }
\index[general]{Making Bacula Use a Single Tape }
\addcontentsline{toc}{subsection}{Making Bacula Use a Single Tape}

Most people will want Bacula to fill a tape and when it is full, a new tape
will be mounted, and so on. However, as an extreme example, it is possible for
Bacula to write on a single tape, and every night to rewrite it. To get this
to work, you must do two things: first, set the VolumeRetention to less than
your save period (one day), and the second item is to make Bacula mark the
tape as full after using it once. This is done using {\bf UseVolumeOnce =
yes}. If this latter record is not used and the tape is not full after the
first time it is written, Bacula will simply append to the tape and eventually
request another volume. Using the tape only once, forces the tape to be marked
{\bf Full} after each use, and the next time {\bf Bacula} runs, it will
recycle the tape. 

An example Pool resource that does this is: 

\footnotesize
\begin{verbatim}
Pool {
  Name = DDS-4
  Use Volume Once = yes
  Pool Type = Backup
  AutoPrune = yes
  VolumeRetention = 12h # expire after 12 hours
  Recycle = yes
}
\end{verbatim}
\normalsize

\subsection*{A Daily, Weekly, Monthly Tape Usage Example}
\label{usageexample}
\index[general]{Daily, Weekly, Monthly Tape Usage Example }
\index[general]{Example!Daily Weekly Monthly Tape Usage }
\addcontentsline{toc}{subsection}{Daily, Weekly, Monthly Tape Usage Example}

This example is meant to show you how one could define a fixed set of volumes
that Bacula will rotate through on a regular schedule. There are an infinite
number of such schemes, all of which have various advantages and
disadvantages. 

We start with the following assumptions: 

\begin{itemize}
\item A single tape has more than enough capacity to do  a full save.  
\item There are 10 tapes that are used on a daily basis  for incremental
   backups. They are prelabeled Daily1 ...  Daily10.  
\item There are 4 tapes that are used on a weekly basis  for full backups.
   They are labeled Week1 ... Week4.  
\item There are 12 tapes that are used on a monthly basis  for full backups.
   They are numbered Month1 ... Month12  
\item A full backup is done every Saturday evening (tape inserted  Friday
   evening before leaving work).  
\item No backups are done over the weekend (this is easy to  change).  
\item The first Friday of each month, a Monthly tape is used for  the Full
   backup.  
\item Incremental backups are done Monday - Friday (actually  Tue-Fri
   mornings). 
   \end{itemize}

We start the system by doing a Full save to one of the weekly volumes or one
of the monthly volumes. The next morning, we remove the tape and insert a
Daily tape. Friday evening, we remove the Daily tape and insert the next tape
in the Weekly series. Monday, we remove the Weekly tape and re-insert the
Daily tape. On the first Friday of the next month, we insert the next Monthly
tape in the series rather than a Weekly tape, then continue. When a Daily tape
finally fills up, {\bf Bacula} will request the next one in the series, and
the next day when you notice the email message, you will mount it and {\bf
Bacula} will finish the unfinished incremental backup. 

What does this give? Well, at any point, you will have a the last complete
Full save plus several Incremental saves. For any given file your want to
recover (or your whole system), you will have a copy of that file every day
for at least the last 14 days. For older versions, you will have at least 3
and probably 4 Friday full saves of that file, and going back further, you
will have a copy of that file made on the beginning of the month for at least
a year. 

So you have copies of any file (or your whole system) for at least a year, but
as you go back in time, the time between copies increases from daily to weekly
to monthly. 

What would the Bacula configuration look like to implement such a scheme? 

\footnotesize
\begin{verbatim}
Schedule {
  Name = "NightlySave"
  Run = Level=Full Pool=Monthly 1st sat at 03:05
  Run = Level=Full Pool=Weekly 2nd-5th sat at 03:05
  Run = Level=Incremental Pool=Daily tue-fri at 03:05
}
Job {
  Name = "NightlySave"
  Type = Backup
  Level = Full
  Client = LocalMachine
  FileSet = "File Set"
  Messages = Standard
  Storage = DDS-4
  Pool = Daily
  Schedule = "NightlySave"
}
# Definition of file storage device
Storage {
  Name = DDS-4
  Address = localhost
  SDPort = 9103
  Password = XXXXXXXXXXXXX
  Device = FileStorage
  Media Type = 8mm
}
FileSet {
  Name = "File Set"
  Include = signature=MD5 {
    fffffffffffffffff
  }
  Exclude = { *.o }
}
Pool {
  Name = Daily
  Pool Type = Backup
  AutoPrune = yes
  VolumeRetention = 10d   # recycle in 10 days
  Maximum Volumes = 10
  Recycle = yes
}
Pool {
  Name = Weekly
  Use Volume Once = yes
  Pool Type = Backup
  AutoPrune = yes
  VolumeRetention = 30d  # recycle in 30 days (default)
  Recycle = yes
}
Pool {
  Name = Monthly
  Use Volume Once = yes
  Pool Type = Backup
  AutoPrune = yes
  VolumeRetention = 365d  # recycle in 1 year
  Recycle = yes
}
\end{verbatim}
\normalsize

\subsection*{ Automatic Pruning and Recycling Example}
\label{PruningExample}
\index[general]{Automatic Pruning and Recycling Example }
\index[general]{Example!Automatic Pruning and Recycling }
\addcontentsline{toc}{subsection}{Automatic Pruning and Recycling Example}

Perhaps the best way to understand the various resource records that come into
play during automatic pruning and recycling is to run a Job that goes through
the whole cycle. If you add the following resources to your Director's
configuration file: 

\footnotesize
\begin{verbatim}
Schedule {
  Name = "30 minute cycle"
  Run = Level=Full Pool=File Messages=Standard Storage=File
         hourly at 0:05
  Run = Level=Full Pool=File Messages=Standard Storage=File
         hourly at 0:35
}
Job {
  Name = "Filetest"
  Type = Backup
  Level = Full
  Client=XXXXXXXXXX
  FileSet="Test Files"
  Messages = Standard
  Storage = File
  Pool = File
  Schedule = "30 minute cycle"
}
# Definition of file storage device
Storage {
  Name = File
  Address = XXXXXXXXXXX
  SDPort = 9103
  Password = XXXXXXXXXXXXX
  Device = FileStorage
  Media Type = File
}
FileSet {
  Name = "Test Files"
  Include = signature=MD5 {
    fffffffffffffffff
  }
  Exclude = { *.o }
}
Pool {
  Name = File
  Use Volume Once = yes
  Pool Type = Backup
  LabelFormat = "File"
  AutoPrune = yes
  VolumeRetention = 4h
  Maximum Volumes = 12
  Recycle = yes
}
\end{verbatim}
\normalsize

Where you will need to replace the {\bf ffffffffff}'s by the appropriate files
to be saved for your configuration. For the FileSet Include, choose a
directory that has one or two megabytes maximum since there will probably be
approximately 8 copies of the directory that {\bf Bacula} will cycle through. 

In addition, you will need to add the following to your Storage daemon's
configuration file: 

\footnotesize
\begin{verbatim}
Device {
  Name = FileStorage
  Media Type = File
  Archive Device = /tmp
  LabelMedia = yes;
  Random Access = Yes;
  AutomaticMount = yes;
  RemovableMedia = no;
  AlwaysOpen = no;
}
\end{verbatim}
\normalsize

With the above resources, Bacula will start a Job every half hour that saves a
copy of the directory you chose to /tmp/File0001 ... /tmp/File0012. After 4
hours, Bacula will start recycling the backup Volumes (/tmp/File0001 ...). You
should see this happening in the output produced. Bacula will automatically
create the Volumes (Files) the first time it uses them. 

To turn it off, either delete all the resources you've added, or simply
comment out the {\bf Schedule} record in the {\bf Job} resource. 

\subsection*{Manually Recycling Volumes}
\label{manualrecycling}
\index[general]{Volumes!Manually Recycling }
\index[general]{Manually Recycling Volumes }
\addcontentsline{toc}{subsection}{Manually Recycling Volumes}

Although automatic recycling of Volumes is implemented in version 1.20 and
later (see the 
\ilink{Automatic Recycling of Volumes}{_ChapterStart22} chapter of
this manual), you may want to manually force reuse (recycling) of a Volume. 

Assuming that you want to keep the Volume name, but you simply want to write
new data on the tape, the steps to take are: 

\begin{itemize}
\item Use the {\bf update volume} command in the Console to  ensure that the
   {\bf Recycle} field is set to {\bf 1}  
\item Use the {\bf purge jobs volume} command in the Console  to mark the
   Volume as {\bf Purged}. Check by using  {\bf list volumes}. 
   \end{itemize}

Once the Volume is marked Purged, it will be recycled the next time a Volume
is needed. 

If you wish to reuse the tape by giving it a new name, follow the following
steps: 

\begin{itemize}
\item Use the {\bf purge jobs volume} command in the Console  to mark the
   Volume as {\bf Purged}. Check by using  {\bf list volumes}.  
\item In Bacula version 1.30 or greater, use the Console  {\bf relabel}
   command to relabel the Volume. 
   \end{itemize}

Please note that the relabel command applies only to tape Volumes. 

For Bacula versions prior to 1.30 or to manually relabel the Volume, use the
instructions below: 

\begin{itemize}
\item Use the {\bf delete volume} command in the Console  to delete the Volume
   from the Catalog.  
\item If the a different tape is mounted, use the {\bf unmount}  command,
   remove the tape, and insert the tape to be  renamed.  
\item Write an EOF mark in the tape using the following  commands: 

   \footnotesize
\begin{verbatim}
  mt -f /dev/nst0 rewind
  mt -f /dev/nst0 weof
\end{verbatim}
\normalsize

where you replace {\bf /dev/nst0} with the appropriate  device name on your
system.  
\item Use the {\bf label} command to write a new label to  the tape and to
   enter it in the catalog. 
   \end{itemize}

Please be aware that the {\bf delete} command can be dangerous. Once it is
done, to recover the File records, you must either restore your database as it
was before the {\bf delete} command, or use the {\bf bscan} utility program to
scan the tape and recreate the database entries.