Event ID - 509

Event Id509
SourceESE
DescriptionA request to read from the file %2 at offset %3 for %4 bytes succeeded, but took an abnormally long time (%5 seconds) to be serviced by the OS. In addition, %6 other I/O requests to this file have also taken an abnormally long time to be serviced since the last message regarding this problem was posted %7 seconds ago. This problem is likely due to faulty hardware. Please contact your hardware vendor for further assistance diagnosing the problem.
Event InformationAccording to Microsoft:
EXPLANATION:
This Warning event is logged when the Exchange database engine tries to write to the named file and encounters a delayed response from the operating system in performing that write operation. This is a warning, not an error, because the operation eventually finishes, although it is slow. This might indicate a hardware problem, probably with the disk controller, a disk, or other storage component.
USER ACTION:
Because this event typically indicates a problem with your disk subsystem or other server hardware, you should carefully examine the performance of the hardware in your Exchange server environment. If available, run hardware diagnostics provided by the server manufacturer. If there are specific tests available to test the disk subsystem, run those tests also. Running these hardware tests may help you discover the cause of the performance bottleneck. If the server uses a SAN device, make sure that the SAN has been configured correctly.
Reference LinksExchange (ESE)

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