Oct 022022

So, there’s a common problem where when performing a backup, you’ll see it fail with Veeam Unable to Truncate Microsoft SQL Server transaction logs.

This is usually due to permission problems either with the account used for guest processing, or with permissions inside of your SQL database. Typically in most cases this can be resolved by referencing the appropriate Veeam KB article which outlines the permissions required for proper guest processing of Microsoft SQL servers.

However, in some rare cases you may have everything configured properly, however the backup may continue to present these warnings with where it’s unable to truncate Microsoft SQL Server transaction logs.

The Problem

I recently deployed an SQL Server in a domain, and of course made sure to setup the proper backup procedures as I’ve done a million times.

However, when performing a backup, the backup would present a warning with the following message:

Error message on Veeam backup, Unable to Truncate Microsoft SQL Server transaction logs
Veeam Backup Warning – Unable to Truncate Microsoft SQL Server transaction logs.
Unable to truncate Microsoft SQL Server transaction logs. Details: Failed to call RPC function 'Vss.TruncateSqlLogs': Error code: 0x80004005. Failed to invoke func [TruncateSqlLogs]: Unspecified error. Failed to process 'TruncateSQLLog' command. Failed to logon user [ReallyLongDomainName\Admin-Account]. Win32 error:The user name or password is incorrect. Code: 1326.

This was very odd as I configured everything properly, and even confirmed it when referring the Veeam KB listed above in this post.

So I decided to look at this as if it was something different, something with credentials, or a different problem.

I noticed that in this specific customer environment, that their FQDN for their domain was so long, that the NETBIOS domain name did not equal their FQDN domain name.

In this example, the following was observed:

FQDN: LongCompanyName.com

Due to the length of the domain, they shortened the NETBIOS domain with abbreviated letters.

When configuring the Veeam credentials for guest processing, one would assume that when using the “AD Search” function, it would have pulled the “LCNDOMAIN\BackupAdminProcessing” account, however when using the check feature, it actually created an entry for “LongCompanyName\BackupAdminProcessing”, which was technically incorrect as it didn’t match the SAM logon format for the account.

The Fix

Because of the observation noted above, I created a manual credential entry for “LCNDOMAIN\BackupAdminProcessing”, reconfigured the backup job to use those new credentials, and it worked!

The issue is because when using the AD search function in the credential manager, Veeam doesn’t translate and pull the NETBIOS domain, but uses the SAM logon format and assumes the UPN Domain matches the NETBIOS domain name.

While this may hold true in most scenarios, there may be rare situations (like above) where the NETBIOS domain name does not match the domain used in the UPN suffix.

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