When a logical drive's Write Cache Policy is set to Write Thru, write performance to the logical drive may be negatively impacted and can cause frame drops during video ingest or capture.
The cache battery is required to have a minimum 72 hour hold time to backup data written to the logical drives. When the cache battery hold time is less than 72 hours, if Adaptive Writeback Cache is enabled, the Current Write Cache Policy will change from Write Back to Write Thru for safer operation.
Write Cache Policy
- Write Back – Data is written first to the cache, then to the logical drive for better performance. The Promise VTrak has a cache backup battery to protect data in the cache from a sudden power failure.
- Write Thru – Also written as “Write Through”. Data is written to the cache and the logical drive at the same time for safer operation. No battery backup is needed since data is written to the drives immediately.
If your Write Cache Policy is set to Write Back, the write cache setting automatically changes to Write Thru when all of the following conditions occur:
- The logical drive Write Cache Policy is set to Write Back.
- The Adaptive Writeback Cache feature is enabled.
- The cache backup battery is offline, removed, dead, reconditioning, or otherwise has less than 72 hours of hold time.
Reconditioning the battery helps maintain battery fitness. The reconditioning process will completely discharge and then fully recharge the cache battery.
During reconditioning, if the Adaptive Writeback Cache function is enabled, the controller cache is set to Write Thru. After reconditioning, and if the battery hold time is greater than 72 hours, the cache is reset to Write Back.
By default, reconditioning the battery will happen on the 1st of every month at 2:00 AM. This time may not be the most convienent schedule for some installations.
Battery reconditioning can be scheduled for a more convienet time via WebPAM PROe.
NOTE If Adaptive Writeback Cache is disabled, it does not mean the Vtrak will not hold anything in cache in the event of a power failure. In fact, the batteries will power the cache for the amount of time specified in "Estimated Hold Time".
For example, if Adaptive Writeback Cache is disabled and the battery displays 69 hours left for the hold time, whatever is held in cache will be flushed to disk as long as the Vtrak is powered on within the 69 hour window.
Scheduling Battery Reconditioning
- Log-in to WebPAM PROe.
- In the left hand window, click on the Subsystem icon or IP address of the VTrak.
- Now click on the Scheduler tab in the right side window.
- Click on Battery Reconditioning from the activity list.
- The scheduling menu will show.
- If Battery Reconditioning is not in the list, you will need to schedule this activity.
- Click on the down arrow to the right of the Scheduler tab.
- Select Add Battery Reconditioning Schedule from the drop down menu.
- The scheduling menu will show.
- Adjust the schedule to a convenient time.
- This example below will recondition batteries on the first Saturday of every month at 2:00 AM.
- You may also enable or disable the scheduled event by clicking the Enable This Schedule box.
- Once the schedule is configured, click Submit to save changes.