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Chapter 13. How to use the Amanda file-driver

Stefan G. Weichinger

Original text;XML-conversion;Updates
AMANDA Core Team

Table of Contents

Introduction
Possible Uses
Setup
Basics
Recovery

Note

Refer to http://www.amanda.org/docs/howto-filedriver.html for the current version of this document.

This document covers the use of the file-driver in Amanda 2.4.3 and higher.

Examples given here have been taken from a SuSE-Linux-8.2-Pro-environment, using Amanda 2.4.4p1 and the snapshot 2.4.4p1-20031202. Please adjust paths, configuration names and other parameters to your system.

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 man amanda, section OUTPUT DRIVERS, for more information on its implementation. As the name suggests, this driver uses files as virtual (or file) tapes. Once created and labeled, these file tapes can be selected and changed with the standard tape-changer-interface of the Amanda server.

Possible Uses

  • test installations

    You can easily explore the rich features of Amanda on systems without tape drives.

  • cheap 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.

  • disk-based installations

    You can use the file-driver to backup onto a set of file tapes hosted on a bunch of hard-disks or a RAID-system. Combined with another Amanda-configuration that dumps the file 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.

Setup

Basics

This guide assumes you have setup the basic Amanda-services as described in Amanda Installation Notes

The configuration in this HOWTO is called "daily". The file tapes are also called vtapes in this document, which stands for "virtual tapes".

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

Before beginning you will need to decide on (a) dedicated part(s) of your hard disk(s) for your file 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.

Steps

  1. Prepare the filesystem(s) used for the tapes.

    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.

  2. 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.

  3. 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.

  4. 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-tarball. 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.

    chg-disk was introduced with the snapshot 20031202. 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.

    Note

    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.

  5. Set up your tape-config.

    In the general section you have to set the parameters tapecycle , tapetype , tpchanger , changerfile , tapedev , rawtapedev and changerdev.

    Example:

            $ 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".

    Note

    The parameter changerdev is NOT needed with chg-disk as it is not parsed by chg-disk.
  6. Create the virtual tapes.

    Note

    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 -|
    	               |- info
    	               |- data -> slot1/
    	               |- slot1/
    	               |- 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 
    	

  7. 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.

    	Usage: amlabel [-f] <conf> <label> [slot <slot-number>] 
    	

    Example:

    	$ 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.

  8. Test your setup with amcheck.

    Run amcheck daily (or, more general, amcheck <config>) and look for anything Amanda complains about.

    A proper output looks like:

    	$ amcheck daily
    	Amanda Tape Server Host Check
    	--
    	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.

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...) "