Learn Bacula - Pool, Volume & Storage

#Introduction

In episode 5, the FileSet determined which files are backed up. In episode 6 we answer the next question: where is the backup data stored and for how long? The answer is Pool, Volume, and Storage — the three media concepts that most often confuse new administrators.

Think of a volume as a cassette: one media unit where data is written. A Pool is the cassette rack grouped by role (daily backup, monthly backup, restore). Storage is the cassette player — the device that actually writes to the media. Understanding these three layers prevents the classic mistake of backups overwriting data that hasn't expired yet.

#Pool and Volume

#Volume

A volume is the media unit where data is written. In disk storage, one volume is one file with a name like FilePool-0001 in the storage directory. Each volume has a label, unique and recorded by Bacula in the catalog. When a volume is full, Bacula automatically uses the next one.

#Pool

A Pool is a collection of volumes with the same characteristics — especially retention. Pools are created in bacula-dir.conf:

Pool {
  Name = FilePool
  Pool Type = Backup
  Recycle = yes
  AutoPrune = yes
  Volume Retention = 30 days
  Maximum Volume Bytes = 20 GB
  Maximum Volumes = 100
}

The key parameters:

• Pool Type = Backup — marks the pool for backup data (not restore).
• AutoPrune = yes — Bacula automatically removes volume records that have passed retention.
• Recycle = yes — pruned volumes can be reused (recycled) with a new label.
• Volume Retention = 30 days — how long a volume's contents are kept before it can be recycled.
• Maximum Volume Bytes — the size limit of one volume; when reached, Bacula moves to a new volume.
• Maximum Volumes — the maximum number of volumes in the pool; if full and all still active, jobs wait or fail.

#Retention: Recycle and AutoPrune

This is the heart of media management. The flow:

1. A volume holds backups until it passes Volume Retention.
2. With AutoPrune = yes, stale volume records are removed from the catalog when a prune job runs.
3. With Recycle = yes, pruned volumes get a new label and are used again for new data.

Retention has three distinct layers (covered in detail in episode 7): File Retention (file metadata in the catalog), Job Retention (job records), and Volume Retention (how long media survives). To preserve data, Volume Retention must be >= Job Retention >= File Retention.

* list pools
* list volumes pool=FilePool

From here you see every volume: status (Append, Full, Recyclable), bytes used, and when it was last used.

#Storage Device

The Device resource in bacula-sd.conf describes the physical media. The two main types:

#File Storage (disk)

Device {
  Name = FileStorage
  MediaType = File
  Archive Device = /var/lib/bacula/storage
  LabelMedia = yes
  Random Access = yes
  AutomaticMount = yes
  RemovableMedia = no
  AlwaysOpen = no
}

• Random Access = yes — the media can be accessed randomly (disk), so restore is much faster.
• RemovableMedia = no — the media cannot be removed; it is always available.
• LabelMedia = yes — Bacula may automatically label new volumes when needed.

#Tape Storage

Device {
  Name = TapeDrive
  MediaType = LTO-9
  Archive Device = /dev/nst0
  LabelMedia = yes
  Random Access = no
  AutomaticMount = yes
  RemovableMedia = yes
  AlwaysOpen = no
}

• Random Access = no — tape is sequential; restore requires scanning the media.
• RemovableMedia = yes — tape can be removed and archived on a shelf.

We dive deeper into tape and changers in episode 11.

#Labeling and Mounting Media

#label

New media must be labeled before it can be used. From bconsole:

* label barcodes pool=FilePool

label barcodes reads the tape barcode (if any) or creates a label automatically. To give an explicit name:

* label

bconsole asks for the volume name, pool, and storage. On disk storage with LabelMedia = yes, labeling often happens automatically when a job needs a volume — but understanding the manual commands still matters for control.

#mount

Mount the media (especially tape) before use:

* mount storage=TapeDrive
* unmount storage=TapeDrive

On disk storage, AutomaticMount = yes makes mounting automatic — you'll rarely need manual mount. On tape, mount/unmount are important daily operations.

#Storage Status

Monitor media health through bconsole:

* status storage=FileStorage
* status device

The output shows the device, mounted volume, and whether the device is in use by a job. If a job fails because a device is unavailable, this command is the first diagnostic step.

#Closing

Key takeaways:

• Volume = media unit (one file on disk, one tape); Pool = a group of volumes with the same retention.
• AutoPrune removes stale records; Recycle allows volumes to be reused.
• Volume Retention decides how long media survives — set it longer than your restore needs.
• File devices = random access, non-removable; Tape devices = sequential, removable.
• label prepares new media; mount/unmount manage mounting; status storage checks health.

In the next episode, episode 7, we'll schedule backups and understand job types — the Schedule resource with Run = Full Mon at 22:00 and Run = Incremental Tue-Sun at 22:00, the Backup/Restore/Verify/Admin job types, plus the three retention layers (File, Job, Volume) and the auto-prune mechanism. This is what makes backups run on their own without human intervention.