Disk Repository

The sizing for local disk repositories (DAS, SAN, NAS) varies depending on the stored data. The provided formulas are based on experiences but may vary depending on your individual data.

Additionally, please read about Teams data.

Exchange Data

The provided formula is applicable to both item-level and snapshot-based repositories.

For primary mailboxes

(Current primary mailboxes total size) + ((Daily change rate * 2) * (Days of retention)) + (10% working area)

For archive mailboxes

(Current archive mailboxes total size) + ((Daily change rate) * (Days of retention)) + (10% working area)

If you run an existing M365 or on-premise Exchange use the PowerShell commandlets Get-Mailbox and Get-MailboxStatistics on your infrastructure to get input to the following formulas.

You can get the Total size of current primary mailboxes with Get-Mailbox and Total size of current archive mailboxes with Get-Mailbox -Archive.

The following example returns the size of all primary mailboxes and can be adapted for archive mailboxes using the -Archive option:

Get-Mailbox | Get-MailboxStatistics | Select-Object DisplayName, ItemCount, TotalItemSize | Format-Table –autosize

In the field we, typically experience daily change rates ranging from 0.2 to 1%. For normal mailbox backups, the change rate is multiplied by 2 due to archiving and file versioning, consuming additional backup space. Alternatively, this factor can be calculated more optimistically with 1.5.

During the backup processing, “transaction protocols and database checkpoints” can consume up to 10% of the repository space, which is calculated as the workspace.

SharePoint and OneDrive Data

You can view current and previous data usage for SharePoint Online and OneDrive for Business in the Microsoft 365 Admin Center. For SharePoint navigate to Reports > Usage > SharePoint > Site Usage > Storage. Keep in mind that this information only reflects your current cloud usage, and the backup on disk will be larger due to metadata and backed-up item versions.

This data allows you to estimate the daily change rate and the total source data size for this formula. When calculating the repository size, consider the ‘total data size’ to be the planned size, including anticipated growth and migrations.

The formula for SharePoint and OneDrive data is the same, as (OneDrive for Business is essentially SharePoint under the hood).

(Total data size) + ((Daily change rate) * (Days of retention)) + (10% working area)

Based on our field experience, we observe daily change rates of about 0.5% to 1%.

To manage and limit the overall backup size, consider reducing the number of item versions in document libraries and lists.

Bitlocker encryption

Bitlocker encryption of volumes used to store backup data is fully supported, and we did not recognize a major impact on “backup and restore” times when working with such volumes. However, if you want to encrypt or decrypt a volume, we recommend not running any restore or backup processes on this volume in parallel, as it can significantly impact the performance of the Bitlocker process.

Jet database files

The local Veeam Backup for Microsoft 365 “VB365” Repository comprises multiple folders, each created for every year of retention. Within each year folder, there are one or more Jet-based repository files (.adb) along with a transaction and check log (.jrs and .chk). Each .adb file has a maximum size of 64 TB. To circumvent this limit, an automatic rule triggers the generation of a new repository file in the same storage location when it reaches 59 TB. For example, a three-year retention results in three folders, each containing one or multiple .adb files, with each file capable of growing up to approximately 60 TB.