I’ve seen a number of cases where Exchange Information Stores are located on SANs. If you don’t have enough throughput you’re likely to see RPC request timeouts for the database, mailboxes or even a server. This typically correlates to Event IDs of 10025, 10026 and 10027. If a mailbox is having such problems then it will be quarantined. If you have this happen once or twice then it’s likely not that big of a deal. However, if it happens repeatedly then you’ve likely got a problem. These can be cumbersome to fix. So while you’re working on things, rather than have mailboxes go offline all the time, you can edit the registry to turn off the time-out detection that causes quarantining of assets. To do so, open regedit and backup your registry. Once done, locate the following key (assuming the server name is KRYPTEDEX2010:
\\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\KRYPTEDEX2010
Right-click the name of the server, click on New, and create a “DWORD (32-bit) Value” with a name of DisableTimeoutDetection. Set the value to 1 and save. All done. Good luck fixing your I/O (and don’t treat the symptom without curing the disease or you’ll end up having to isinteg your database eventually).