Cannot extract mailbox messages from the Exchange backup error

I am backing up my Exchange 2010 which is on a Windows 2008 R2 server. Full backups seem to be succeeding with GRT turned on. However, sometimes on my incremential backups I am getting this: 

Final error: 0xe0000393 - Cannot extract mailbox messages from the Exchange backup. Review the job log for more information.

Then below that in the logs I see this for two databases being backed up: 

V-79-57344-915 - Unable to complete the operation. The following error was returned when opening the Exchange Database file: '-1022 There is a disk IO error. '

Not sure why.