The site collection could not be restored. If this problem persists, please make sure the content databases are available and have sufficient free space

Topology details:

-SharePoint Server 2010 with latest CU

-SQL Server 2008R2

-4 applications and 7 WFE’s

Problem Details:  Requirement comes up to replicate the production site collection to staging environment. We have taken the backup of the site by using PowerShell command without any issues.As soon as we started the restore command then it throws the following exception.

Error Message:

The site collection could not be restored. If this problem persists, please make sure the content databases are available and have sufficient free space.

Note:  One thing we need to understand that this is a very generic error message and does not have any correlation with the disk space available or not. If you have disk space available on the SQL Server as well as on the servers where SP is running then also you will face this error message. I think this is a BUG but not getting any documentation based on this to conclude the same. 

Troubleshooting done:

-Check the disk space on the SQL Server where LDF and MDF files are stored.

-Check the partition on the SQL SERVER in reference to data files

-Make sure the content database has enough space allocated.

-Make sure the databases does not have restrictive growth

-Make sure to check the disk space on the SP server where restore is running.  Approximately it should 2 times the DB size.

Resolution Applied:

-Go to “SQL Server Properties--Connections” and uncheck ‘Use query governor to prevent long-running queries’. Also, set “Remote query timeout” to 0.

-Stop and restart the "Windows SharePoint service Timer" 

-Restart IIS

If you have any queries/questions regarding the above mentioned information then please let me know.

I would be more than happy to help you as well as resolves your issues, thank you.