6.2. Bacula Features Bacula has a number of features that differentiate it from other open-source backup systems. Here is an overview of these features:
SQL catalog -
The catalog contains a list of files that have been backed up, the basic attributes of each file, including a checksum, the client each file came from, and the volumes where files are stored. Because of this, the catalog is absolutely vital to backups and restores: it stores the records of what has been backed up and when. Although the included bscan tool can help reconstruct the catalog should it be damaged, the catalog should, in general, be backed up separately after each backup cycle.
Multivolume backups -
One of Bacula's differentiating features is its excellent native support for multi-volume backups. When equipped with an autochanger, Bacula can simply span tapes without any human intervention (and, if properly configured, can label new volumes on the fly to support this goal). Even on a single-drive machine, Bacula automatically prompts, either via the console or email, for the next tape when it requires additional media.
Flexible media support -
Bacula can back up to different types of media, using disk or tape equally easily. SCSI autochangers simply work "out of the box." Bacula includes tools for easy transfer of backups to CD (bimagemgr) or DVD (dvd-handler), and the replaceable autochanger support allows very large storage silos to be integrated with Bacula with a modicum of effort.
Backup levels -
As with most other backup systems, Bacula differentiates between full backups (complete dumps), differential backups (files changed since last full backup), and incremental backups (changed files since the last backup of any sort). The desired backup level is specified in the definition or schedule of a backup job, and can be overridden if a job is manually submitted. If a full backup is scheduled, but no full backup is present in the catalog, Bacula automatically promotes a differential or incremental backup job to a full backup job.
Bacula storage format -
All data backed up by Bacula is stored on volumes. A volume is simply a repository for backup data; it may be a tape, optical media, or a simple file. Bacula uses a unique format rather than a standard format such as tar or dump. This design choice ensures consistency across platforms and implementations of Bacula. Consider the use of tar for an archive format. Although GNU tar is the tar present on most Linux implementations, other vendors may use a different implementation, and these implementations are not always compatible with each other, which can then create difficulty unpacking an archive created on a different platform. Bacula avoids this problem by completely specifying the storage format. While this design choice has distinct advantages, it also means that specialized tools are required to extract data from Bacula backups in the absence of a working Bacula installation. In general, it is best to use a working Bacula director, catalog, and console to recover files. However, Bacula does provide the bls and bextract standalone utilities for last-resort recovery when the database is not available. The volume format is thoroughly documented in the Bacula source code and the developer's guide. The block design of Bacula's storage implementation also allows interleaving of files, which can allow multiple file daemons to communicate with a storage daemon simultaneously, although this slows down file restore by causing more seeks within a storage volume.
Multiple pool support -
Backup media in Bacula is drawn from pools, which are essentially lists of available media volumes that can be selected for use. In a small configuration, one pool may be sufficient, but Bacula also supports multiple pools and multiple backup devices extremely well. By supporting multiple pools, Bacula allows easy classification of different machine types or different data handling requirements into different backup pools. An ongoing project will allow migration of job data between pools; this is discussed in the section "Future Directions" later in this chapter.
Macintosh HFS+ support -
As of version 1.38.2, Bacula supports resource forks on Macintosh HFS+ volumes; this support allows for correct backup and restoration of files that use resource as well as data forks, and is completely transparent to the user.
Windows VSS support -
The Bacula 1.38 Win32 client is Volume Shadow Copy Service-aware; this allows consistent backup of open Windows files, which makes backing up Windows systems a great deal easier and more reliable. Note that VSS support is present only in Windows XP and Windows Server 2003 and later. There is no VSS support for Windows 95, 98, ME, NT, or 2000: this is a Windows limitation, not a Bacula limitation.
Standalone recovery -
Bacula makes it quite easy to create a bootable Linux CD containing everything necessary to bring up a system from bare metal and begin restoration of files. Slightly more difficult (but still efficacious) processes exist for Solaris, FreeBSD, and Windows systems. This is discussed in a bit more detail in the section "Advanced Features" later in this chapter.
Documentation -
Documentation is the Achilles' heel of many open-source projects. Thankfully, this is not the case with Bacula. Although the organization of the manual at the time of writing is a bit lacking, Bacula is thoroughly and accurately documented.
Scalability -
Bacula is designed to be an enterprise-class backup system. Because it has clearly defined, logically separated components, it is possible to easily grow a Bacula installation to a very large size indeed. The modular design promotes easy scaling of a site's backup architecture as it grows: in general, adding capacity is simply a matter of defining additional file daemons or storage daemons and adding them to the director's configuration. Much work has gone into making Bacula interoperable with many enterprise-class tape silos and label conventions so that it can coexist with large commercial data management and operations. Despite its suitability for very large networks, Bacula's configuration is simple enough that it is perfectly reasonable to use Bacula to back up a very small network or even just a single machine. Bacula is equally happy backing up 300 clients to a huge tape silo, or one laptop to a weekly burned DVD.
Tape drive testing -
One of the most commonly asked questions of Bacula (and probably any other backup system) is "Will it work with my tape drive?" While the online manual does have a good number of drives known to work well, a far more authoritative answer can be obtained using the btape utility. This program reads the configuration you have defined for your tape drives and uses it to run a comprehensive series of compatibility tests, including reading, writing, and various seek operations. If btape completes all testing successfully, you can be confident that your tape drive is both compatible with Bacula and correctly configured. |
