During restore restart, an I/O error occurred on checkpoint file Short version: Running a RESTORE VERIFYONLY throws one of these errors:


  During restore restart, an I/O error occurred on checkpoint file '\Server\Backup\SQLDirectBackup\DatabaseName\RestoreCheckpointDB24.CKP' (operating system error 5(Access is denied.)). The statement is proceeding but cannot be restarted. Ensure that a valid storage location exists for the checkpoint file.


Or


  During restore restart, an I/O error occurred on checkpoint file '\Server\Backup\SQLDirectBackup\DatabaseName\RestoreCheckpointDB11.CKP' (operating system error (null)). The statement is proceeding but cannot be restarted. Ensure that a valid storage location exists for the checkpoint file.


More information:


Using Ola's SQL Server Maintenance Solution
The file share is on a Dell DR4300 device 
Has occurred on multiple servers using this device for backup storage
Different servers, service accounts, versions of SQL Server have all thrown this error
Not consistent or reproducible as far as I can tell (happened Monday &amp; Wednesday but not Tuesday)
Subsequent runs of the backup jobs have succeeded without error
Time of day does not seem to be relevant, it's occurred at all hours
The error is not immediate, it occurs minutes into the execution of the command
Default backup directory points to \\Server\Backup\SQLDirectBackup\DatabaseName\
Hasn't happened with an actual restore yet... but I'd like to avoid that. Hence the post.


I've never seen this error before, and all my research is coming up empty. It is possible that this has been happening for a long time but I am new to the company and only recently added Severity 16+ alerting so I cannot be sure.

Anyone have any ideas? Safe to ignore? Potential time bomb? I'm stumped.
Anyone have any ideas? Safe to ignore? Potential time bomb? I'm
  stumped.


It's not a "bomb", this means only that if you want to use RESTORE with RESTART option (to complete interrupted RESTORE ) you'll not be able to do it, i.e. checkpoint file cannot be used and the RESTORE will not be able to skip some passes if they woudl be done prior to interruption.

You can read more about checkpoint file here: Restores using Invalid Backup Default Locations

The cause of this error is that your default backup location becomes temporarily inaccessible.

You can just ignore this error or you can change the default backup location with any local path.