| Event Id | 491 |
| Source | ESE98 |
| Description | <process name> (<process id>) An attempt to determine the minimum I/O block size for the volume "<name>" containing "<file name>" failed with system error <error code>: "<error message>". The operation will fail with error <error code>. |
| Event Information | According to Microsoft: CAUSE: This issue can occur if you do not have the appropriate permissions on the Mdbdata folder to mount the mailbox or public store. RESOLUTION: To resolve this issue, open to the Exchange Server folder, and then grant the following default permissions for the Mdbdata folder: • Administrators: Full Control • Authenticated Users: Read and Execute, List Folder Contents, Read • Creator Owner: None • Server Operators: Modify, Read and Execute, List Folder Contents, Read, Write • System: Full Control To mount the affected mailbox or public store, start Exchange System Manager, right-click the mailbox or public store, and then click Mount Store. |
| Reference Links | XADM: Cannot Mount Mailbox or Public Store and Event ID 491 Occurs |
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