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What are the Workarounds to the Server I/O Performance Degradation Caused by the S5100 BBU Failure?

Publication Date:  2012-07-20 Views:  72 Downloads:  0
Issue Description
During the S5100 BBU maintenance, the old BBU is replaced with a new one. After this, users can detect BBU alarm messages after logging in to the Web OSM. Meanwhile, high CPU wa and low I/O performance are also detected by executing the vmstat command on a SUSE Linux server. Alarm information: By logging in to the S5100 Web OSM, BBU alarm messages stating unknown battery status are detected.
Alarm Information
None
Handling Process
Step 1 Log in to the S5100 Web OSM, and then click the manual recovery button for each BBU alarm message to clear the alarms. Step 2 Complete the initial battery charge and discharge for enabling the S5100 to properly identify the battery status. After that, the failback information is generated and the cache write policy is changed from write through to write back. Step 3 Observe the CPU resource consumption on the server, where you can see that the I/O performance of the S5100 is restored to normal.
Root Cause
This problem is caused by the battery status detection mechanism of the S5100. Specifically, when a new BBU is inserted but has not completed the initial charge and discharge, the S5100 cannot determine the battery status and then generate BBU alarm messages. In this condition, the S5100 regards the battery status as faulty and thus enters the safe mode to change the cache write policy from write back to write through, degrading I/O performance of the S5100.
Suggestions
To ensure that the status of a new BBU can be properly identified by the S5100, complete the initial charge and discharge for the BBU. After this, the battery needs to be partially discharged and charged every three months, and fully discharged and charged every year for enabling the storage device to properly identify the battery status. Otherwise, BBU alarm messages stating insufficient charge can be found by logging in to the Web OSM, which however is normal.

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