What should I do when the status of a QES NAS storage pool is “Degraded”?
Applicable Products
QES
Root Cause
When a storage pool has the status “Degraded”, it means one or more RAID groups in the pool are in degraded mode.
All RAID types except for RAID 0 can tolerate a certain number of disk failures without losing data. If one or more disks fail within a RAID group but the RAID type of the group can tolerate that number of disk failures, then the RAID group enters degraded mode.
In degraded mode, data can still be read from and written to the RAID group but usually with lower performance.
Solution
QES automatically tries to recover RAID groups from degraded mode by replacing any failed disks with healthy spare disks.
QES uses a global hot spare system, where every free disk installed in the NAS with the status “Ready” is considered to be a spare disk.
If a disk failure occurs in a RAID group, QES immediately replaces the failed disk with a spare disk and then starts rebuilding the RAID group. If there are no free disks available, then you must install a new drive in the NAS. QES will start rebuilding the RAID group after it detects the new drive.
- The performance of a storage pool will be decreased while a RAID group in the pool is rebuilding.
- Increasing the number of disks in a RAID group increases the risk of simultaneous disk failure and lengthens rebuild times.
- When creating a storage pool with a large number of disks, you should split the disks into sub-groups using RAID 50 or RAID 60.
