Veeam Backup Repository Explained

The repository can use different types of storage depending on the environment and backup design.

What is Stored in the Repository?

The repository can contain the backup files discussed in the previous articles:

For example:

The actual files and structure can vary depending on the backup method and Veeam configuration.

Why Repository Capacity Matters

When planning a Veeam Backup Repository, it is important to estimate how much storage will actually be required. The calculation should consider the size of the protected VMs, daily change rate, backup frequency, retention policy, and backup method. Veeam also recommends looking at the block-level daily change rate because incremental backups contain changed blocks rather than the entire VM data.

A simple way to estimate the required capacity is:

Required Storage
≈ Full Backup
+ Incremental Backups
+ Additional Space

Example

Assume we have:

Number of VMs       : 10 VMs
Average VM size     : 500 GB
Total VM data       : 5 TB
Daily change rate   : 5%
Retention           : 7 restore points

First, calculate the estimated daily change:

5 TB × 5%
= 250 GB per day

So, approximately 250 GB of new backup data may be generated every day.

For 7 restore points:

250 GB × 7
= 1.75 TB

If we assume the resulting full backup stored in the repository is approximately 3 TB after the configured backup processing, a simple estimate would be:

Full Backup       = 3.00 TB
7 Incrementals    = 1.75 TB
--------------------------------
Estimated Storage = 4.75 TB

However, 4.75 TB should not be treated as the final repository size.

Additional free space is required for operations such as Active Full, Synthetic Full, merge operations, and normal data growth. Veeam specifically notes that merge operations can require additional free space, and capacity planning should account for variations in backup size.

A more practical design could therefore look like:

Backup data             = 4.75 TB
Additional working space = 3.00 TB
Safety margin            = 1.50 TB
-----------------------------------
Recommended capacity     ≈ 9.25 TB

The exact amount will depend on the backup method, retention configuration, workload and actual backup file growth. There is no magical Veeam formula where you type "10 VMs" and the universe politely returns "8.73 TB". Backup data has the unfortunate habit of changing.

What Can Increase Repository Usage?

Several factors can increase the amount of storage required:

For example, a VM with a 10% daily change rate will consume considerably more incremental storage than one with a 2% daily change rate, even if both VMs have the same capacity.

VM Size = 1 TB

2% Change Rate
    ↓
20 GB/day

10% Change Rate
    ↓
100 GB/day

Over 30 days, the difference becomes significant:

20 GB × 30 = 600 GB

100 GB × 30 = 3 TB

This is why daily change rate is one of the most important numbers when sizing a backup repository. Veeam recommends measuring actual change rates rather than simply estimating from the VM's provisioned capacity.

Don't Fill the Repository to 100%

It is also important to maintain sufficient free space on the repository. Running a repository close to full capacity can cause backup or merge operations to fail.

Veeam's documentation notes that merge operations require additional space, and recommends ensuring sufficient free space for these operations.

A good practical approach is:

Repository Capacity
        │
        ├── Backup Data
        │
        ├── Retention Growth
        │
        ├── Full / Synthetic Operations
        │
        └── Free Space / Safety Margin

Simple Rule

When sizing a repository, start with these five numbers:

1. Total protected data
2. Daily change rate
3. Backup frequency
4. Retention period
5. Backup method

Then add working space and a safety margin instead of sizing the repository exactly to the calculated backup data.

Veeam ONE can also be used for capacity planning by analyzing historical repository usage and forecasting how many days remain before the repository runs out of space.

"The goal is not just to have enough space for today's backups. The repository should have enough capacity to handle retention, backup operations, growth, and unexpected increases in data change."

Repository vs Backup Files

It is useful to understand the difference:

Backup Repository

The storage location managed by Veeam.

Backup Files

The actual files stored inside the repository, such as VBK and VIB.

Think of it like this:

Key Points

• A Veeam Backup Repository is the destination for backup data.
• It stores backup files such as VBK, VIB, and VBM.
• Repository capacity must account for retention and backup growth.
• Repository performance affects backup and restore operations.
• Synthetic Full and merge operations can generate additional repository I/O.
• Monitoring free space and repository performance is important for reliable backups.