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(Virtual tapes with chg-disk)
(Comparison chg-disk and chg-multi / Disk requirements / consistent examples)
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Stefan G. Weichinger, November - December, 2003 ; minor updates in April, 2005.
Stefan G. Weichinger, November - December, 2003 ; minor updates in April, 2005.
==Introduction==
==Introduction==


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The virtual tapes are also called "vtapes" in this document.
The virtual tapes are also called "vtapes" in this document.
==Disk requirements==
Before beginning you will need to decide on dedicated parts of your hard disks for your virtual tape storage. While this space could be spread among several file systems and hard disks, I recommend to dedicate at least a specific partition, better a specific physical harddisk to the task of keeping your vtapes. The use of a dedicated disk will speed things up definitely.
The disk space you dedicate for your vtapes should NOT be backed up by Amanda. Also, for performance reasons there should be NO holding disks on the same partition as the vtapes, preferably not even on the same physical drive.
If you only have one harddisk, it will work out, too, but you will suffer low performance due to massive head-moving in your harddisk, resulting from copying data between the filesystems.
===Prepare the filesystem used for the vtapes===
Decide on where to put your files, create the appropriate partition(s) and
filesystem(s) and mount them. In our example we have the dedicated partition hdc1, mounted on /amandatapes for vtape storage.  The filesystem must also be capable of creating large file (> 4Gbyte) and must be able to handle symlinks (no vfat).
$ mount
[...]
/dev/hdc1 on /amandatapes type reiserfs (rw)
[...]
Make sure there is space left. Determine the amount of space you will use.
$ df -h /amandatapes
Filesystem      Size  Used  Avail  Use%  Mounted on
/dev/hdc1        20G    0G    20G    0%  /amandatapes
In our example we have 20GB diskspace left on /amandatapes.
===Determine length and number of tapes===
After deciding on the number of vtapes you want to create, evenly allocate the available space among them.
Look at the following rule of thumb: As many filesystems exhibit dramatically reduced performance when they are nearly full I have chosen to allocate only 90% of the available space. So we have:
      (Available Space * 0.9) >= tapelength * tapecycle
This is a very conservative approach to make sure you don´t suffer any performance drop due to a nearly-full-filesystem.
As it is uncommon for Amanda to fill an entire tape you may also wish to use more space than that.
So you could determine possible combinations of tapelength/tapecycle with the more general formula:
      Available Space >= tapelength * tapecycle
In our example we take the conservative approach, and so we could create the following combinations:
:20 GB * 0.9 = 18 GB to use
:* 18 GB = 18 GB * 1
:* 18 GB = 9 GB * 2
:* 18 GB = 6 GB * 3
:* 18 GB = 3 GB * 6
:* 18 GB = ...
Using only one tape is generally considered a bad idea when it comes to backup, so we should use at least 3 tapes (for testing purposes), better 6 or more tapes.
:* 18 GB = 3 GB * 6
so we get the value 3 GB for the tapelength if we want to use 6 tapes.
===Create a tapetype definition===
Add a new tapetype definition similar to the following to your amanda.conf. I named my definition "HARD-DISK". Choose whatever name you consider appropriate.
define tapetype HARD-DISK {
    comment "Dump onto hard disk"
    length 3072 mbytes # specified in mbytes to get the exact size of 3GB
}
You don´t have to specify the parameter speed (as it is commonly listed in tapetype definitions and reported by the program amtapetype). Amanda does not use this parameter right now.
There is also an optional parameter filemark, which indicates the amount of space "wasted" after each tape-listitem. Leave it blank and Amanda uses the default of 1KB.
The tapetype defined above should just be choosen by the paramater '''tapetype''' in amanda.conf too:
  tapetype HARD-DISK


==Simple virtual tapes==
==Simple virtual tapes==


A virtual tape is implemented as a directory with a subdirectory named "data" in it:
A virtual tape is implemented as a directory with a subdirectory named "data" in it. Let's create one for our "test" configuration:


  $ mkdir -p /space/vtapes/tape1/data
# chown amanda:disk /amandatapes
# chmod 750 /amandatapes                      # backups contain secret files!
# su - amanda
  $ mkdir -p /amandatapes/test/tape1/data


This tape can be manipulated by the [[ammt]] command, a replacement for the system command "mt". The
This tape can be manipulated by the [[ammt]] command, a replacement for the system command "mt". The
ammt command understands the different output drivers from Amanda:
ammt command understands the different output drivers from Amanda:


  $ ammt -f file:/space/vtapes/tape1 status
  $ ammt -f file:/amandatapes/test/tape1 status
  $ ammt -f file:/space/vtapes/tape1 rewind
  $ ammt -f file:/amandatapes/test/tape1 rewind


Vtapes are always non-rewinding.  Just like Amanda needs them.  That's why you always need to rewind it when you want to start reading a vtape from the beginning.
Vtapes are always non-rewinding.  Just like Amanda needs them.  That's why you always need to rewind it when you want to start reading a vtape from the beginning.
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amdd command also can specify an upperlimit on the virtual tapesize with the '''-l''' option:
amdd command also can specify an upperlimit on the virtual tapesize with the '''-l''' option:


  $ amdd -l 200k if=/dev/urandom of=file:/space/vtapes/tape1 bs=32k
  $ amdd -l 200k if=/dev/urandom of=file:/amandatapes/test/tape1 bs=32k
  amdd: write error: No space left on device
  amdd: write error: No space left on device
  8+0 in
  8+0 in
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When you want to read it, just mount is as a "data" directory, or even simpler, create a symlink "data" pointing to the mounted cdrom.
When you want to read it, just mount is as a "data" directory, or even simpler, create a symlink "data" pointing to the mounted cdrom.


  $ rm -r /space/vtapes/tape1/data
  $ rm -r /amandatapes/test/tape1/data
  $ ammt -f file:/space/vtapes/tape1 status
  $ ammt -f file:/amandatapes/test/tape1 status
  file:/space/vtapes/tape1: status: OFFLINE
  file:/amandatapes/tape1: status: OFFLINE
  $ ln -s /media/cdrom /space/vtapes/tape1/data
  $ ln -s /media/cdrom /amandatapes/test/tape1/data
  $ ammt -f file:/space/vtapes/tape1 status
  $ ammt -f file:/amandatapes/test/tape1 status
  file:/space/vtapes/tape1: status: ONLINE
  file:/amandatapes/test/tape1: status: ONLINE


Amanda cannot write a to cdrom, but can use it as a read protected vtape.  (But ''you'' can write a cdrom from the contents of the data directory with another program.)
Amanda cannot write a to cdrom, but can use it as a read protected vtape.  (But ''you'' can write a cdrom from the contents of the data directory with another program.)
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We can use such a vtape as a tape device in amanda.conf with a line like:
We can use such a vtape as a tape device in amanda.conf with a line like:
   
   
  tapedev file:/space/vtapes/tape1
  tapedev file:/amandatapes/test/tape1


And then point the data subdirectory each day to a different place.
And then point the data subdirectory each day to a different place.
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Amanda can use many virtual tapes, and operate the bunch of vtapes by a virtual tape changer.
Amanda can use many virtual tapes, and operate the bunch of vtapes by a virtual tape changer.


Create 5 vtapes:
Create 5 vtapes for our "test" configuration:


  for i in 1 2 3 4 5; do mkdir -p /space/vtapes/tape$i/data; done
  for i in 1 2 3 4 5; do mkdir -p /amandatapes/test/tape$i/data; done


Now we a server with 5 tape drives. They are virtual tapes, but Amanda isn't picky about that.
Now we a server with 5 tape drives. They are virtual tapes, but Amanda isn't picky about that.
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  firstslot 1
  firstslot 1
  lastslot 5
  lastslot 5
  slot 1 file:/space/vtapes/tape1
  slot 1 file:/amandatapes/test/tape1
  slot 2 file:/space/vtapes/tape2
  slot 2 file:/amandatapes/test/tape2
  slot 3 file:/space/vtapes/tape3
  slot 3 file:/amandatapes/test/tape3
  slot 4 file:/space/vtapes/tape4
  slot 4 file:/amandatapes/test/tape4
  slot 5 file:/space/vtapes/tape5
  slot 5 file:/amandatapes/test/tape5


Run "amcheck test" to verify we did not make an error somewhere,
Run "amcheck test" to verify we did not make an error somewhere,
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  tpchanger "chg-disk"
  tpchanger "chg-disk"
  changerfile "/home/amanda/test/chg-disk-status"    # status files prefix
  changerfile "/home/amanda/test/chg-disk-status"    # status files prefix
  tapedev "file:/space/vtapes/slots"
  tapedev "file:/amandatapes/test/slots"
  tapecycle 5
  tapecycle 5
  # changerdev is ignored
  # changerdev is ignored
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symlink:
symlink:


  $ mkdir -p /space/vtapes/slots
  $ mkdir -p /amandatapes/test/slots
  $ cd /space/vtapes/slots
  $ cd /amandatapes/test/slots
  $ for i in 1 2 3 4 5; do mkdir -p slot$i; done
  $ for i in 1 2 3 4 5; do mkdir -p slot$i; done
  $ ln -s slot1 data
  $ ln -s slot1 data
  $ ammt -f file:/space/vtapes/slots status
  $ ammt -f file:/amandatapes/test/slots status


The file "info" in the slot_root_dir is created automatically on first use.
The file "info" in the slot_root_dir is created automatically on first use.
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  $ amtape test reset
  $ amtape test reset


==Setup==
==Comparison of chg-disk and chg-multi for virtual tapes==
 
This guide assumes you have setup the basic Amanda services as described in Amanda Installation Notes.
 
The configuration in this HOWTO is called "daily".
 
Before beginning you will need to decide on dedicated parts of your hard disks for your virtual tape storage. While this space could be spread among several file systems and hard disks, I recommend to dedicate at least a specific partition, better a specific physical harddisk to the task of keeping your vtapes. The use of a dedicated disk will speed things up definitely.
 
The disk space you dedicate for your vtapes should NOT be backed up by Amanda. Also, for performance reasons there should be NO holding disks on the same partition as the vtapes, preferably not even on the same physical drive.
 
If you only have one harddisk, it will work out, too, but you will suffer low performance due to massive head-moving in your harddisk, resulting from copying data between the filesystems.
 
* Prepare the filesystem used for the vtapes. Decide on where to put your files, create the appropriate partition(s) and
filesystem(s) and mount them. In our example we have the dedicated partition hdc1, mounted on /amandatapes for vtape storage.
 
$ mount
[...]
/dev/hdc1 on /amandatapes type reiserfs (rw)
[...]
Make sure there is space left. Determine the amount of space you will use.
 
$ df -h /amandatapes
Filesystem      Size  Used  Avail  Use%  Mounted on
/dev/hdc1        20G    0G    20G    0%  /amandatapes
 
In our example we have 20GB diskspace left on /amandatapes.
 
* Determine length and number of tapes. After deciding on the number of vtapes you want to create, evenly allocate the
available space among them.
 
Look at the following rule of thumb: As many filesystems exhibit dramatically reduced performance when they are nearly full I have chosen to allocate only 90% of the available space. So we have:
 
      (Available Space * 0.9) >= tapelength * tapecycle
 
This is a very conservative approach to make sure you don´t suffer any performance drop due to a nearly-full-filesystem. As it is
uncommon for AMANDA to fill, or almost fill an entire tape you may also wish to use more space than that.  So you could determine
possible combinations of tapelength/tapecycle with the more general formula:
 
      Available Space >= tapelength * tapecycle
 
In our example we take the conservative approach:
:* 20 GB * 0.9 = 18 GB to use
and so we could create the following combinations:
:* 18 GB = 18 GB * 1
:* 18 GB = 9 GB * 2
:* 18 GB = 6 GB * 3
:* 18 GB = 3 GB * 6
:* 18 GB = ......... you get the picture.
 
Using only one tape is generally considered a bad idea when it comes to backup, so we should use at least 3 tapes (for testing purposes), better 6 or more tapes.
:* 18 GB = 3 GB * 6
so we get the value 3 GB for the tapelength if we want to use 6 tapes.
 
* Create a tapetype definition. Add a new tapetype definition similar to the following to your amanda.conf. I named my definition "HARD-DISK". Choose whatever name you consider appropriate.
 
define tapetype HARD-DISK {
      comment "Dump onto hard disk"
      length 3072 mbytes # specified in mbytes to get the exact size of 3GB
}
You don´t have to specify the parameter speed (as it is commonly listed in tapetype definitions and reported by the program amtapetype). AMANDA does not use this parameter right now.
 
There is also an optional parameter filemark, which indicates the amount of space "wasted" after each tape-listitem. Leave it blank and AMANDA uses the default of 1KB.
 
* Think about tapechangers.
 
As you will use a set of vtapes, you have to also use a kind of vtape-changer. There are several tape-changer-scripts included in the AMANDA. Read more about tape-changer-scripts in AMANDA Tape Changer Support. Right now there are two scripts that can be used with vtapes. These scripts take different approaches to the handling of tapes.
:*The script chg-multi handles many drives with a tape in each drive.
:*The script chg-disk handles a library with one drive and multiple tapes.
 
So with vtapes you could look at it this way: chg-multi simulates multiple tape drives with one tape in each drive. chg-disk simulates one tape-library with multiple tapes in. As chg-multi exists for a much longer time than chg-disk, it is still used in many AMANDA-vtape-installations.
 
Contrary to chg-multi, which is a generic changer-script that must be somewhat adjusted to the use of the file-driver, chg-disk offers exactly the behavior needed for handling vtapes. IMHO the approach is much more logical, so I recommend to use chg-disk in new AMANDA-vtape-installations.
   
      To use chg-disk you need to have at least amanda-2.4.4p1-20031202.
 
Choose the one that fits your way of vtape-handling and -maintenance.  In this HOWTO I only cover the use of chg-disk. Usage of
chg-multi is pretty similar and will maybe covered in a later version of this document.
 
* Set up your tape-config. In the general section of amanda.conf, you have to set the parameters tapecycle , tapetype , tpchanger , changerfile , tapedev , rawtapedev and changerdev.
 
$ vi /usr/local/etc/amanda/daily/amanda.conf
...
 
tapecycle 6
tapetype HARD-DISK
tpchanger "chg-disk"
changerfile "/usr/local/etc/amanda/daily/changer"
tapedev  "file:/amandatapes/daily"
This reflects the use of your defined tapetype.  The parameter tapecycle tells AMANDA how much tapes can be used, Set this value according to the number of tapes you want to use. The parameter tapetype , points to the tapetype definition you have created before.  The parameter tpchanger tells AMANDA to use the generic tape-changer-script to handle the vtapes. You can think of it as a virtual tape-changer-device.
 
The parameter changerfile is used to give chg-disk the "prefix" for the "%s-changer, %s-clean, %s-slot" files it needs. Use something like "changer" in your config-dir. Please note that this file does NOT have to exist, but it won't hurt anyway.  The parameter tapedev tells the chg-disk-script where the root-dir for your vtapes is.
 
In our example the vtape-files go to /amandatapes.  To separate multiple configurations, we decided to use subdirectories according to the configuration name "daily".
      The parameter changerdev is NOT needed with chg-disk as it is not parsed by chg-disk.
 
* Create the virtual tapes.
 
      Gene Heskett has committed a shell-script which creates and labels the vtapes in one step. Stefan G. Weichinger will
      generalize this script and contribute it, this script will just read your settings in amanda.conf and create the
      appropriate vtape-directories.
 
Now you have to create the tape-directories. chg-disk needs a directory structure like:


slot_root_dir -|
The two changers chg-disk and chg-multi have a different approach to the handling of tapes:
                |- info
* The script chg-multi handles many drives with a tape in each drive.
                |- data -> slot1/
* The script chg-disk handles a library with one drive and multiple tapes.
                |- slot1/
This implies that chg-disk can drive only one tape at a time, while in the setup with chg-multi, you can always specify one specific vtape, and use that one for e.g. restoring, while amdump is using another vtape.
                |- slot2/
                |- ...
                |- slotn/
where 'slot_root_dir' is the tapedev 'file:xxx' parameter and 'n' is the tapecycle parameter.
 
So in our example we do:
$ mkdir /amandatapes/daily
for the 'slot_root_dir' and
    $ mkdir /amandatapes/daily/slot1
    $ mkdir /amandatapes/daily/slot2
      .... 
 
for the virtual slots that will later contain the vtapes. If you have many vtapes to create and their names follow a pattern you may be able to do them all with a single loop such as:
 
$ for n in 1 2 3 4 5 6 7 8 9 10 11 12
> do
>    mkdir /amandatapes/daily/slot${n}
> done
Create the info-file:
$ touch /amandatapes/daily/info
 
and link the first slot to the data-file (to "load" the vtape into the first slot):
$ ln -s /amandatapes/daily/slot1 /amandatapes/daily/data
 
Make sure the AMANDA-user has write-permissions on these directories:
$ chown -R amanda_user /amandatapes
$ chgrp -R amanda_group /amandatapes
$ chmod -R 750 /amandatapes
* Label the virtual tapes. As the virtual tapes are handled just like physical tapes by the AMANDA-Server they have to be
labeled before use.
 
$ amlabel daily daily1 slot 1
  ....
$ amlabel daily daily2 slot 2
  .... 
 
If you have many vtapes to label and their names follow a pattern you may be able to do them all with a single loop such as:
 
$ for n in 1 2 3 4 5 6 7 8 9 10 11 12
> do
>    amlabel daily daily${n} slot ${n}
> done
Label all your created tapes according to the "labelstr"-parameter in your amanda.conf. Consult the amlabel-man-page for details.


* Test your setup with amcheck. Run amcheck daily (or, more general, amcheck <config>) and look for anything AMANDA complains about.
While the chg-disk changer is very straightforward to set up, the chg-multi script has a wider range of uses, but also is slightly more complicated to set up.  The chg-multi script can e.g. be extended to  [[rait]], making a mirror of the backup to a real tape or a vtape on an external disk at the same time.


A proper output looks like:
For chg-multi, the underlying filesystem does not need to be able to handle symlinks. You can use plain old VFAT on an external USB-disk that is also accessible by Windows.  (But you'll need to limit the maximum tapesize to 4 Gbyte, or using multi-tape-split dumps (available in 2.5.0) to avoid running into another limit.)


$ amcheck daily
If you don't need the complexity of chg-multi, stay with the easy chg-disk. Migrating to chg-multi
Amanda Tape Server Host Check
is easy by just moving the '''slotX''' directories of the chg-disk vtape tree to the '''data''' directories of each vtape in the chg-multi tree.
--
  Holding disk /amhold: 6924940 KB disk space available,
that's plenty
amcheck-server: slot 2: date 20031115 label daily02
(exact label match)
NOTE: skipping tape-writable test
Tape daily02 label ok
Server check took 0.377 seconds


Recheck your files if errors occur.
To use chg-disk you need to have at least amanda-2.4.4p1-20031202.


==Recovery==
==Recovery==


Recovering files from vtapes is very similar to recovering files from a "real" tapechanger. Make sure you read the chapter Restore.  
Recovering files from vtapes is very similar to recovering files from a "real" tapechanger.
Make sure you read the chapter Restore.  
I will simply paste a amrecover-session here (provided by JC Simonetti, author of chg-disk):
I will simply paste a amrecover-session here (provided by JC Simonetti, author of chg-disk):


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  Extracting files using tape drive file:/BACKUP2/slots/ on host
  Extracting files using tape drive file:/BACKUP2/slots/ on host
  backupserver.local. Load tape B3_14 now
  backupserver.local.  
Load tape B3_14 now
  Continue [?/Y/n/s/t]? Y
  Continue [?/Y/n/s/t]? Y
  . /etc/passwd
  . /etc/passwd
Line 374: Line 290:
  200 Good bye.   
  200 Good bye.   


Nothing spectacular? The trick is this: When AMANDA asks you
Nothing spectacular? The trick is this: When Amanda asks you


  Load tape B3_14 now  
  Load tape B3_14 now  

Revision as of 00:05, 17 December 2005

Stefan G. Weichinger, November - December, 2003 ; minor updates in April, 2005.

Introduction

Since release 2.4.3 Amanda supports the usage of a output driver called "file". See the manual page of amanda, section OUTPUT DRIVERS, for more information.

As the name suggests, this driver uses files on disk as virtual tapes. Amanda can write to and read from virtual tapes, just like real tapes. A bunch of virtual tapes can even be manipulated with a changer.

Possible Uses

  • Test installations: You can easily explore the rich features of Amanda on systems without tape drives. Virtual tapes are usually also much faster than many real tape drives.
  • Inexpensive installations: Without buying a tape drive you can enjoy the benefits of Amanda and backup to a bunch of harddisks. You can create CD/DVD-sized backups which you can burn onto optical disks later. Or you can backup to external disks connected with Firewire or USB.
  • disk-based installations: You can use the file driver to backup onto a set of virtual tapes hosted on a bunch of hard-disks or a RAID-system. Combined with another Amanda configuration that dumps the virtual tapes to real tapes, you can provide reliable backup with faster tapeless recovery. This is called "disk-to-disk-to-tape" backup by some people today.

Please be sure to understand the differences between holding disks and virtual tapes. The two serve different purposes; holding disks allow for parallelism of multiple disklist entries (DLE's) being backed up while virtual tapes are a replacement for physical tapes.

The virtual tapes are also called "vtapes" in this document.

Disk requirements

Before beginning you will need to decide on dedicated parts of your hard disks for your virtual tape storage. While this space could be spread among several file systems and hard disks, I recommend to dedicate at least a specific partition, better a specific physical harddisk to the task of keeping your vtapes. The use of a dedicated disk will speed things up definitely.

The disk space you dedicate for your vtapes should NOT be backed up by Amanda. Also, for performance reasons there should be NO holding disks on the same partition as the vtapes, preferably not even on the same physical drive.

If you only have one harddisk, it will work out, too, but you will suffer low performance due to massive head-moving in your harddisk, resulting from copying data between the filesystems.

Prepare the filesystem used for the vtapes

Decide on where to put your files, create the appropriate partition(s) and filesystem(s) and mount them. In our example we have the dedicated partition hdc1, mounted on /amandatapes for vtape storage. The filesystem must also be capable of creating large file (> 4Gbyte) and must be able to handle symlinks (no vfat). 

$ mount
[...]
/dev/hdc1 on /amandatapes type reiserfs (rw)
[...]

Make sure there is space left. Determine the amount of space you will use. 

$ df -h /amandatapes
Filesystem      Size  Used  Avail  Use%   Mounted on
/dev/hdc1        20G    0G    20G    0%   /amandatapes

In our example we have 20GB diskspace left on /amandatapes.

Determine length and number of tapes

After deciding on the number of vtapes you want to create, evenly allocate the available space among them.

Look at the following rule of thumb: As many filesystems exhibit dramatically reduced performance when they are nearly full I have chosen to allocate only 90% of the available space. So we have: 

     (Available Space * 0.9) >= tapelength * tapecycle

This is a very conservative approach to make sure you don´t suffer any performance drop due to a nearly-full-filesystem. As it is uncommon for Amanda to fill an entire tape you may also wish to use more space than that. So you could determine possible combinations of tapelength/tapecycle with the more general formula: 

     Available Space >= tapelength * tapecycle

In our example we take the conservative approach, and so we could create the following combinations:

20 GB * 0.9 = 18 GB to use
  • 18 GB = 18 GB * 1
  • 18 GB = 9 GB * 2
  • 18 GB = 6 GB * 3
  • 18 GB = 3 GB * 6
  • 18 GB = ...

Using only one tape is generally considered a bad idea when it comes to backup, so we should use at least 3 tapes (for testing purposes), better 6 or more tapes.

  • 18 GB = 3 GB * 6

so we get the value 3 GB for the tapelength if we want to use 6 tapes.

Create a tapetype definition

Add a new tapetype definition similar to the following to your amanda.conf. I named my definition "HARD-DISK". Choose whatever name you consider appropriate. 

define tapetype HARD-DISK {
    comment "Dump onto hard disk"
    length 3072 mbytes 	# specified in mbytes to get the exact size of 3GB
}

You don´t have to specify the parameter speed (as it is commonly listed in tapetype definitions and reported by the program amtapetype). Amanda does not use this parameter right now.

There is also an optional parameter filemark, which indicates the amount of space "wasted" after each tape-listitem. Leave it blank and Amanda uses the default of 1KB.

The tapetype defined above should just be choosen by the paramater tapetype in amanda.conf too: 

 tapetype HARD-DISK

Simple virtual tapes

A virtual tape is implemented as a directory with a subdirectory named "data" in it. Let's create one for our "test" configuration: 

# chown amanda:disk /amandatapes
# chmod 750 /amandatapes                       # backups contain secret files!
# su - amanda
$ mkdir -p /amandatapes/test/tape1/data

This tape can be manipulated by the ammt command, a replacement for the system command "mt". The ammt command understands the different output drivers from Amanda: 

$ ammt -f file:/amandatapes/test/tape1 status
$ ammt -f file:/amandatapes/test/tape1 rewind

Vtapes are always non-rewinding. Just like Amanda needs them. That's why you always need to rewind it when you want to start reading a vtape from the beginning.

Basic writing to a vtape can be done with amdd, a replacement for the system command "dd". Virtual tapes have no real builtin capacity; the upper limit is "diskspace, the final frontier". However Amanda does obey the size you specify in tapetype definition of a vtape in amanda.conf. The amdd command also can specify an upperlimit on the virtual tapesize with the -l option: 

$ amdd -l 200k if=/dev/urandom of=file:/amandatapes/test/tape1 bs=32k
amdd: write error: No space left on device
8+0 in
6+1 out

The above command writes 200 Kbytes of garbage (6 full blocks of 32k + 1 partial block) on the vtape before it bumps into the end of the virtual tape.

When there is no "data" subdirectory in a vtape, the vtape is "offline". You could burn the contents of the data directory to a CD-R, and store that away. When you want to read it, just mount is as a "data" directory, or even simpler, create a symlink "data" pointing to the mounted cdrom. 

$ rm -r /amandatapes/test/tape1/data
$ ammt -f file:/amandatapes/test/tape1 status
file:/amandatapes/tape1: status: OFFLINE
$ ln -s /media/cdrom /amandatapes/test/tape1/data
$ ammt -f file:/amandatapes/test/tape1 status
file:/amandatapes/test/tape1: status: ONLINE

Amanda cannot write a to cdrom, but can use it as a read protected vtape. (But you can write a cdrom from the contents of the data directory with another program.)

We can use such a vtape as a tape device in amanda.conf with a line like: 

tapedev file:/amandatapes/test/tape1

And then point the data subdirectory each day to a different place.

Virtual tapes with chg-multi

Amanda can use many virtual tapes, and operate the bunch of vtapes by a virtual tape changer.

Create 5 vtapes for our "test" configuration: 

for i in 1 2 3 4 5; do mkdir -p /amandatapes/test/tape$i/data; done

Now we a server with 5 tape drives. They are virtual tapes, but Amanda isn't picky about that.

The "chg-multi" changer uses many tapes drives to emulate a tape changer. Vtapes can also be used here. Change amanda.conf for the "test" configuration to have these values: 

tpchanger "chg-multi"
changerfile "chg-multi.conf"       # name of the special configuration file
# tapedev is ignored if present, to avoid confusion, just comment it out
# changerdev is ignored too

And add a file in the same directory as amanda.conf with the name we specified above as the changerfile chg-multi.conf. Because "chg-multi" is useful in a wide context, we need to specify a lot of parameters that are irrelevant for vtapes: 

multieject 0
needeject 0
gravity 0
ejectdelay 0
statefile /home/amanda/test/changerstatus
firstslot 1
lastslot 5
slot 1 file:/amandatapes/test/tape1
slot 2 file:/amandatapes/test/tape2
slot 3 file:/amandatapes/test/tape3
slot 4 file:/amandatapes/test/tape4
slot 5 file:/amandatapes/test/tape5

Run "amcheck test" to verify we did not make an error somewhere, and we label the tapes in all the slots: 

$ for i in 1 2 3 4 5; do amlabel test TEST-$i slot $i; done
...
$ amtape test show
$ amtape test reset

And we are ready to use our tape changer with 5 tape drives.

Virtual tapes with chg-disk

  • To use chg-disk you need to have at least amanda-2.4.4p1-20031202.

Another changer script "chg-disk" is specifically written to handle a bunch for virtual tapes on disk. This script does not need a separate configuration file. Instead it uses these parameters in amanda.conf: 

tpchanger "chg-disk"
changerfile "/home/amanda/test/chg-disk-status"    # status files prefix
tapedev "file:/amandatapes/test/slots"
tapecycle 5
# changerdev is ignored

"Chg-disk" operates the virtual changer by pointing the symlink data to another directory, named slotX, where X is the slot number. The directory tree should look like: 

slot_root_dir -|
               |- info
               |- data -> slot1/
               |- slot1/
               |- slot2/
               |- ...
               |- slotN/

"slot_root_dir" is the value of the tapedev parameter, and N is value of tapecycle in amanda.conf. While "chg-multi" had a statusfile parameter in the special configuration file, chg-disk needs the name of the statusfile itself as parameter changerfile in amanda.conf.

We create the virtual slots tree for the chg-disk changer, and set it "online", by creating the "data" symlink: 

$ mkdir -p /amandatapes/test/slots
$ cd /amandatapes/test/slots
$ for i in 1 2 3 4 5; do mkdir -p slot$i; done
$ ln -s slot1 data
$ ammt -f file:/amandatapes/test/slots status

The file "info" in the slot_root_dir is created automatically on first use. Do not add a leading zero to the slot number, chg-disk would not understand that. Create as many slots as you have specified in tapecycle.

And we label the virtual tapes: 

$ for i in 1 2 3 4 5; do amlabel test TEST-$i slot $i; done
$ amcheck test

As always we and with "amcheck test" and solve the issues it complains about. We can verify all the virtual tapes, and load the first tape again, ready for the first amdump run: 

$ amtape test show
$ amtape test reset

Comparison of chg-disk and chg-multi for virtual tapes

The two changers chg-disk and chg-multi have a different approach to the handling of tapes:

  • The script chg-multi handles many drives with a tape in each drive.
  • The script chg-disk handles a library with one drive and multiple tapes.

This implies that chg-disk can drive only one tape at a time, while in the setup with chg-multi, you can always specify one specific vtape, and use that one for e.g. restoring, while amdump is using another vtape.

While the chg-disk changer is very straightforward to set up, the chg-multi script has a wider range of uses, but also is slightly more complicated to set up. The chg-multi script can e.g. be extended to rait, making a mirror of the backup to a real tape or a vtape on an external disk at the same time.

For chg-multi, the underlying filesystem does not need to be able to handle symlinks. You can use plain old VFAT on an external USB-disk that is also accessible by Windows. (But you'll need to limit the maximum tapesize to 4 Gbyte, or using multi-tape-split dumps (available in 2.5.0) to avoid running into another limit.)

If you don't need the complexity of chg-multi, stay with the easy chg-disk. Migrating to chg-multi is easy by just moving the slotX directories of the chg-disk vtape tree to the data directories of each vtape in the chg-multi tree.

To use chg-disk you need to have at least amanda-2.4.4p1-20031202.

Recovery

Recovering files from vtapes is very similar to recovering files from a "real" tapechanger. Make sure you read the chapter Restore. I will simply paste a amrecover-session here (provided by JC Simonetti, author of chg-disk): 

# /usr/local/amanda/sbin/amrecover woo
AMRECOVER Version 2.4.4p3. Contacting server on backupserver.local ... 
220 backupserver AMANDA index server (2.4.4p3) ready.
200 Access OK
Setting restore date to today (2004-10-08)
200 Working date set to 2004-10-08.
Scanning /BACKUP2/holding...
Scanning /BACKUP/holding...
200 Config set to woo.
200 Dump host set to backupserver.local.
Trying disk /tmp ...
$CWD '/tmp/RECOVER' is on disk '/tmp' mounted at '/tmp'.
200 Disk set to /tmp.
Invalid directory - /tmp/RECOVER
amrecover> sethost backupserver.local
200 Dump host set to backupserver.local.
amrecover> setdisk /
200 Disk set to /.
amrecover> cd /etc
/etc
amrecover> add passwd
Added /etc/passwd
amrecover> list
TAPE B3_14 LEVEL 0 DATE 2004-09-26
       /etc/passwd
amrecover> extract

Extracting files using tape drive file:/BACKUP2/slots/ on host
backupserver.local. The following tapes are needed: B3_14

Restoring files into directory /tmp/RECOVER
Continue [?/Y/n]? Y

Extracting files using tape drive file:/BACKUP2/slots/ on host
backupserver.local. 
Load tape B3_14 now
Continue [?/Y/n/s/t]? Y
. /etc/passwd
amrecover> quit
200 Good bye.

Nothing spectacular? The trick is this: When Amanda asks you 

Load tape B3_14 now 
Continue [?/Y/n/s/t]?

you have to run the following in a second terminal: 

$ amtape woo slot 14
amtape: changed to slot 14 on file:/BACKUP2/slots/

This step is necessary to load the proper tape into your virtual changer. Let me express this in a more general way:

When amrecover prompts for the tape it needs to restore the files you requested, you have to "load" the tape it requests. The recommended way to do this is to use amtape. The options that make sense in this context are: 

# amtape
Usage: amtape <conf> <command>
       Valid commands are:
               [...]
               slot <slot #>        load tape from slot <slot #>
               [...]
               label <label>        find and load labeled tape
               [...]

If you know which slot contains the requested tape (for example, if you have tape daily01 in slot 1, tape daily02 in slot 2, and so on) you may use the first option. If you just know the label of the tape you need, use the second option.

To continue the upper example: 

amtape woo slot 14 	        # option 1 OR
amtape woo label B3_14 	# option 2

amtape will return something like: 

amtape: label B3_14 is now loaded.

After this you can return to your amrecover-session and continue restoring your files.

Please be aware of the fact reported by JC Simonetti: " I have never never used the "settape" command of amrecover [with chg-disk] since there's some problems with it (tape not loaded correctly, or impossible to change from tape to tape when restoring data shared accross multiple tapes...) "

!!NEW!!

Since Amanda 2.4.3 you can let amrecover use the complete changer instead of the currently loaded tape too. No need to open a second window to load the correct tape.

For this add in amanda.conf: 

amrecover_do_fsf  yes
amrecover_check_label  yes
amrecover_changer  "changer"

With the last line we give the changer a name, which we can use instead of the tape device in amrecover, when starting the command: 

# /usr/local/amanda/sbin/amrecover woo -d changer

or from inside with the settape command or even: 

Extracting files using tape drive file:/BACKUP2/slots/ on host
backupserver.local. Load tape B3_14 now
Continue [?/Y/n/s/t]? t
New tape device [?]: changer
Using tape "changer" from server backupserver.local.
Continue [?/Y/n/s/t]? y
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