Degraded Mode is a term that refers to the status of a computer running RAID. When the RAID is running correctly and without errors it is often said to running in it’s Optimal state. If one or more of the hard drives in a RAID fail, the RAID may still continue to run, but with severe performance limitations in what is termed Degraded Mode.
A RAID system has 3 main modes of operation:
1. Optimal or OK – All drives are functioning and the RAID runs correctly
2. Degraded or Partially Degraded – One or more of that hard drives in the RAID have failed but the RAID still continues to function with no data loss, but significant restrictions in performance. Confusingly, ‘partially degraded’ and ‘degraded’ mean the same thing.
3. Failed – The RAID has significant problems which prevent it from functioning.
Examples
- A two disk RAID 1 mirrored system with 1 failed drive will be running in degraded mode although there will be no loss in performance.
- A multiple disk RAID 5 with one failed drive will be running in degraded mode. Performance will suffer and data transfer speeds will be significantly reduced but there will be no data loss.
Recovering Systems In Degraded Mode
Recovering a system running in degraded mode is usually straightforward but it has to be done right first time. Failure to recover a system in degraded mode can cause significant issues and substantial data loss.
Often the main cause of failure to restore a system to optimal mode from degraded mode is the result of further errors being encountered on other hard drives that were not apparent at the time.
Be careful with the advice from manufacturer’s helplines. Since Data Clinic’s inception, we’ve literally lost count of the number of people who have come to us for assistance after being given the wrong advice from customer support helplines. Unfortunately, just because the person on the other end of the phone works for the manufacturer’s technical support team doesn’t mean they know what they are doing. Be very wary if they suggest that you format, re-install or rebuild anything on your system.
Links
- Take a look at our information on the Top 5 Things To Avoid when you have a RAID or server failure here: http://www.dataclinic.co.uk/raid-or-server-failure-the-top-5-things-to-avoid/
- More information about our RAID services can be found on our RAID recovery page here: http://www.dataclinic.co.uk/hard-disk-raid-recovery/