Understanding The Battery Subsystem: Dell PowerEdge™ Expandable RAID Controller 2
Installation Guide
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Understanding The Battery Subsystem: Dell™
PowerEdge™ Expandable RAID Controller 2
Installation Guide
| Initial Battery Charge |
• Battery Low Conditions |
• Battery Reconditioning |
• Recovering Data from the Controller's Cache |
The PERC 2 controller contains a pair of replaceable nickel-metal hydride (NiMH) batteries and associated charging/monitoring circuitry designed to preserve the contents of its non-volatile cache memory in the event of a power loss or extended power-off conditions. Power loss can occur due to sudden interruption of power to the server; extended power-off situations can occur during system maintenance, hardware upgrades, etc.
This battery holdover time is dependent on the batteries' charge level and age, and the size of the DIMM. For a list of battery holdover times, see Specifications.
The controller keeps its batteries fully charged by applying a small trickle charge to the batteries during normal operation. If the controller's monitoring circuits determine that the batteries are less than fully charged, it automatically activates the fast charger. The fast charger continues charging the batteries until they reach their full charge. A full charging cycle — from fully discharged to fully charged — typically requires 2-3 hours to complete.
Initial Battery Charge
When you first power up your controller, its batteries will be partially or fully discharged and will require charging. This initial charge time depends on the current charge level of the batteries, and could take anywhere from a few minutes to several hours. You can begin using your controller immediately after initial power up, but be aware that the batteries may not be able to preserve the contents of cache memory for the full holdover time stated previously until they reach full charge.
Battery Low Conditions
Under normal operating conditions, the controller reports its batteries' status as OK. OK means that the batteries are either fully charged, or are charging properly, and have at least 24 hours of holdover time remaining.
Whenever the batteries' holdover time drops below 24 hours (as measured by the batteries remaining capacity), the controller generates a low battery condition.
The PERC 2 host driver displays a battery low condition with a pop-up dialog box warning you of the condition and an event entry in the system's event log (on Windows NT and Windows 2000 systems).
Note:
To avoid the possibility of data loss caused by a power outage
during a low battery condition, the controller automatically flushes its
cache contents to disk and disables further use of the cache until the low
battery condition ends.
Normal Causes of a Battery Low Condition
A low battery condition normally occurs if the controller was in a powered-off state for more than a few hours. If the controller is shut-down properly (as part of normal system shutdown), the controller flushes its cache contents to disk and "disconnects" its batteries from cache memory. The controller continues drawing a small amount of current from the batteries during power-off times, to maintain its battery monitoring and capacity settings. It is normal for the batteries to discharge slightly during power-off times, even though the batteries are not being used to maintain the contents of cache memory.
Note:
The controller will not generate a low battery condition when you
first power up your PERC 2, even if your batteries' holdover time is less
than 24 hours. It reports battery low once the batteries are initially
charged (and the batteries' holdover time drops below 24 hours). As
mentioned earlier, be aware that your batteries may not be able to provide
their minimum holdover time until they reach their initial full charge.
In general, you should closely monitor your PERC 2 controller during a battery low condition to ensure that its battery status returns to normal (OK) within 2-3 hours. Contact your technical support representative if a low battery condition remains on beyond normal charging time; it could indicate a faulty battery.
Battery Reconditioning
At approximately six month intervals, the controller notifies you that a battery reconditioning cycle — a full discharge followed by a recharge of its batteries — is required. A full cycle discharge and recharge is recommended every six months in order to:
- Calibrate the battery monitor circuitry.
- Overcome any long-term degradation of the batteries' capacity caused by trickle-charging the batteries.
Battery reconditioning starts only when you initiate it. This allows you to schedule reconditioning at a time when optimal performance is not needed.
To initiate a battery reconditioning immediately, do one of the following:
To schedule a reconditioning cycle for a future time (on Windows NT only), create an AT batch file with the appropriate CLI command. You should try to complete the reconditioning sometime during the week that follows the first notification you receive. The PERC 2 host driver and FAST will continue to remind you periodically that a reconditioning is still needed, so you won't forget.
Note:
During the reconditioning cycle, which takes approximately 6 to 10
hours, the controller automatically disables cache to ensure that no data is
lost. Performance is degraded during this period. Once the
reconditioning cycle is complete, the cache is restored to its original
settings.
If the system is powered off during a reconditioning, it will be necessary to manually restart the reconditioning. If possible, avoid shutting down the system until the reconditioning cycle completes.
Recovering Data from the Controller's Cache
The PERC 2 controller is designed to ensure no loss of data, even under various failure conditions. The controller's Daughter Card contains both the cache memory (DIMM) and battery subsystem as an integrated unit, allowing the Daughter Card's cache to be preserved even when the Daughter Card is removed from the controller card.
If your system loses power, for example, and the controller is not damaged (and the battery holdover time has not been exceeded), the cache is flushed to disk after the controller finishes its power-on-self-test.
If, however, you determine that your controller suffered a hardware failure — for example, you receive a hardware failure message during the PERC 2 power-on self-test — and data in the cache was not flushed to disk prior to the failure, data remains in the cache. To prevent loss of this data, you must flush the controller's cache, even though the main controller is no longer operational.
Note:
If you suspect a hardware failure, contact yourDell technical
support representative to determine the cause of failure and to see if a
replacement controller is required.
The following sections explain how to determine if data is in the cache, and if data is present, how to retrieve it.
Determining if Data is in the Cache
To determine if there is data in the cache
- Press the small push-button on the edge of the PERC 2 Daughter Card to determine if the DIMM is still being powered by the battery subsystem. (Under normal shutdown, the controller flushes any cached data to disk and disconnects the DIMM from the batteries.)
- If the LED does not light, then the cache contains no valid data. You can safely remove power to the PERC 2 controller and/or Daughter Card without data loss.
- If the LED does light, then the DIMM is still being powered by the batteries, indicating that the cache may contain valid data. Proceed with Recovering Data from the Cache.
Note:
he batteries on the Daughter Card, when fully charged, are
designed to maintain the cache memory for holdover times that are
specified in Specifications. To maximize the protection of the cache,
however, you should maintain power to your PERC 2 controller and
Daughter Card by leaving the controller plugged into a powered PCI slot.
If doing so prevents you from using this system, move your controller to
another system where you can maintain power until you have all of the
parts necessary to complete the repair.
Recovering Data from the Cache
To recover data in the cache the following steps must be followed. These should be done by your Dell technical support representative.
Caution:
Do not remove your Daughter Card from the controller until
your Dell technical support representative is ready to replace your
PERC 2 controller.
- Determine if there is data in the cache, as described in Determining if Data is in the Cache.
- Power off the system, uncable and remove the defective controller and Daughter Card assembly.
- Disconnect the Daughter Card from the faulty controller.
- Attach the Daughter Card to the new PERC 2 controller.
- Install the new PERC 2 controller.
- Reattach the SCSI cables.
- Power on and reboot the system.
- The new controller on start-up will recognize that its cache contains valid disk data and proceed to flush the cache to the disks.
Note:
After the cache has been flushed, the system should be powered off
and the new controller removed. The old Daughter Card from the
damaged controller should then be removed from the new controller. The
DIMM from the old Daughter Card should be installed in the new
Daughter Card, and the new Daughter Card attached to the new
controller.
The damaged controller and its Daughter Card should be returned to Dell
for analysis.
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