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Asset ID: 1-72-1205345.1
Update Date:2011-05-19
Keywords:
Solution Type  Problem Resolution Sure

Solution  1205345.1 :   Sun StorageTek[TM] 2500 Arrays: Write Back Cache Disabled during SMART Battery Learn Cycles  

Related Items 
    

  • Sun Storage 2510 Array
    •  
  • Sun Storage 2540 Array
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  • Sun Storage 2530 Array
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Related Categories 
    

  • GCS>Sun Microsystems>Storage - Disk>Modular Disk - 2xxx Arrays
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The StorageTek[TM] 2500 products all have SMART battery technology that will detect whether a battery is no longer capable of holding sufficient charge. This document how the cache battery behaves during the battery learn cycles.

In this Document
  Symptoms
  Cause
  Solution

Applies to:

Sun Storage 2510 Array - Version: Not Applicable to Not Applicable - Release: N/A to N/A
Sun Storage 2530 Array - Version: Not Applicable to Not Applicable   [Release: N/A to N/A]
Sun Storage 2540 Array - Version: Not Applicable to Not Applicable   [Release: N/A to N/A]
This problem can occur on any platform.

Symptoms

During battery learn cycles, the write back cache is disabled.  This is indicated by the battery status
being changed to Learning.  Also, when the learn cycle starts, the following event is logged in the array:

Severity    : Minor
Date        : Wed Sep 15 10:00:01 EDT 2010
Device      : <array name>
Component   : Tray.85.Controller.A.Battery.A
Type        : LogEvent
Information : Learn Cycle Started
Event Code  : 70.20.491
Aggregated  : No
Description : Sep 15 10:00:01 <array name> Tray.85.Controller.A.Battery.A: [ID 0x7310] NOTICE: Learn Cycle Started

Probable Cause :
The array firmware has logged an informational event.

Recommended Action :
None required.

At the end of the learn cycle, the following event is logged:

Severity    : Minor
Date        : Wed Sep 15 11:54:26 EDT 2010
Device      : <array name>
Component   : Tray.85.Controller.A.Battery.A
Type        : LogEvent
Information : Learn Cycle Completed
Event Code  : 70.20.491
Aggregated  : No
Description : Sep 15 11:54:26 <array name> Tray.85.Controller.A.Battery.A: [ID 0x7311] NOTICE: Learn Cycle Completed

Probable Cause :
The array firmware has logged an informational event.

Recommended Action :
None required.


NOTE: During the entire learn cycle process, the write back cache remains disabled and can lead to performance degradation depending on the I/O workload.

Here are the steps that can be used to list the events using Sun StorageTek[TM] Common Array Manager (CAM).

Using the GUI
  1. Expand "Storage Arrays" in the left menu pane.
  2. Expand your storage array name in the left menu pane.
  3. Expand "Troubleshooting" in the left menu pane.
  4. Click on "Events".
  5. In the right pane, click on the -|-> icon. If you mouse over it, it will state "Advanced Filter".
  6. Set "Event" to Log Events.
  7. Set "Event Type" to Component.
  8. Set "Read the last X Kbytes From Log File" to 100.
  9. Set "String Filter" to Battery.
  10. Click on the "Details" of any alarm that is shown.
  11. Review the "Description Field".
  12. Get the value of the array log event ID from the description
Using the Command Line (CLI)
  1. List all the "Battery" events:

    sscs list -d <array name> -t LogEvent -f Battery event

    Where the location for sscs is:

    Solaris: /opt/SUNWstkcam/bin/
    Linux: /opt/sun/cam/bin/
    Windows: C:\Program Files\Sun\Common Array Manager\bin

    Example:

    # ./sscs list -d 2540a -t LogEvent -f Battery event
    2010-09-14 02:59:51 213875 2540a Tray.85.Controller.A.Battery.A LogEvent
    2010-09-14 03:10:27 213896     2540a Tray.85.Controller.A.Battery.A LogEvent
    2010-09-14 03:10:27 213897     2540a Tray.85.Controller.A.Battery.A LogEvent
    2010-09-15 09:35:24 217905     2540a Tray.85.Controller.A.Battery.A LogEvent
    2010-09-15 09:59:56 217957     2540a Tray.85.Controller.B.Battery.B LogEvent
    2010-09-15 10:00:01 217958     2540a Tray.85.Controller.A.Battery.A LogEvent
    2010-09-15 11:53:27 218189     2540a Tray.85.Controller.B.Battery.B LogEvent
    2010-09-15 11:53:39 218190     2540a Tray.85.Controller.B.Battery.B LogEvent
    2010-09-15 11:54:26 218191     2540a Tray.85.Controller.A.Battery.A LogEvent
    2010-09-15 11:54:39 218192     2540a Tray.85.Controller.A.Battery.A LogEvent


  2. Get the detail for a specific event:

    sscs list -d <array name> event <event id>

    Example:

    # ./sscs list -d 2540a event 217958

    Severity    : Minor
    Date        : Wed Sep 15 10:00:01 EDT 2010
    Device      :     2540a
    Component   : Tray.85.Controller.A.Battery.A
    Type        : LogEvent
    Information : Learn Cycle Started
    Event Code  : 70.20.491
    Aggregated  : No
    Description : Sep 15 10:00:01     2540a Tray.85.Controller.A.Battery.A: [ID 0x7310] NOTICE: Learn Cycle Started

    Probable Cause :
    The array firmware has logged an informational event.

    Recommended Action :
    None required.


    # ./sscs list -d 2540a event 218191

    Severity    : Minor
    Date        : Wed Sep 15 11:54:26 EDT 2010
    Device      : 2540a
    Component   : Tray.85.Controller.A.Battery.A
    Type        : LogEvent
    Information : Learn Cycle Completed
    Event Code  : 70.20.491
    Aggregated  : No
    Description : Sep 15 11:54:26 2540a Tray.85.Controller.A.Battery.A: [ID 0x7311] NOTICE: Learn Cycle Completed

    Probable Cause :
    The array firmware has logged an informational event.

    Recommended Action :
    None required.


Cause

A SMART battery backup unit (BBU) contains battery cells, a charger, a battery gas gauge, a discharge load and control logic. With SMART battery, the controller must periodically perform learn cycles to determine how much capacity is left in the battery. This information allows the controller firmware to determine exactly how long the BBU can hold the cache "up" and take action as needed.

Reference <Document: 1207186.1> SMART Battery Functionality in 2500 and 6000 Arrays.

On the StorageTek[TM] 2500 series, because the charge level is expected to fall below the minimum application capacity, the write back cache must be disabled for the whole learn cycle process and for volumes that require battery support.

Solution

This behavior is a normal design for the 2000 series arrays.

If however the write back cache is required during the time the learn cycle runs, it is possible to modify the variable "Write cache without battery" from FALSE to TRUE for each volume, by using either the Common Array Manager (CAM) Graphical User Interface (GUI) or Command Line (sscs).

NOTE: If a power outage occurs while the "Write cache without battery" is set to TRUE and the "Write cache" is ACTIVE, data remaining in the cache are lost, which can lead to data integrity issue. For this reason, setting the "Write cache without battery" should be used with caution.

Using the CAM GUI
  1. Open a browser to the CAM host: https://<server IP>:6789.
  2. Expand "Storage Systems" menu.
  3. Expand your array name menu.
  4. Click the "Volumes" menu.
  5. Click your volume name.
  6. Change the "Write Cache Without Batteries Enabled" from FALSE to TRUE.
Using the CAM command line
  1. Set the "Write Cache Without Batteries" to TRUE:

    sscs modify -a <arrayname> -b true volume <volume name>


    Where the location for sscs is:

    Solaris: /opt/SUNWstkcam/bin/
    Linux: /opt/sun/cam/bin/
    Windows: C:\Program Files\Sun\Common Array Manager\bin



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