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Forum Discussion
RAID6 resync after drive failure: Data Degraded message
I have a ReadyNAS 528 that is set up for RAID6 using X-RAID, purchased in 2018. Someone else set up the system but they moved on, so I have been maintaining it for the past several years. I had 8 drives installed and one failed a month ago, so I removed it. I figured that running the Balance maintenance operation should move things around to back everything up appropriately but I am still getting a "data DEGRADED" message. I have also tried Scrub and Defrag followed by Balance but that didn't fix it either so clearly something more involved is required. I tried RTFM and searching this forum but wasn't able to find what to do after a drive failure or info about this error message. I want my data to be backed up but mostly I want the machine to flashing its all caps message at me.
8 Replies
I should add that I have 29 TB of free space so I would like to run the system with seven drives rather than purchase a replacement
I have 29 TB of free space so I would like to run the system with seven drives rather than purchase a replacement
At this point, you better care about backup your data....
I had 8 drives installed and one failed a month ago, so I removed it.
You still have single drive redundancy, since you started with RAID-6. But not the two drive redundancy offered by RAID-6.
That is why you see the degraded message. Balancing, scrubbing, etc will not fix it (as you found out). None of those steps restore the original redundancy.
Replacing the failed drive would, but it sounds like you'd rather not.
I would like to run the system with seven drives rather than purchase a replacement
Do you have any experience with the linux command line interface?
I should add that I have 29 TB of free space
What size(s) are the remaining disks?
The “Degraded” status makes sense if the failed drive was simply removed and hasn’t been replaced yet. On a redundant ReadyNAS volume, removing a drive leaves the array degraded until a replacement drive is added and the resync completes. Balance, Scrub, and Defrag aren’t substitutes for rebuilding the missing RAID member. I’d check the volume status and logs first, then replace the failed drive with a suitable disk and let the RAID resync. I’d also make sure there’s a current backup before doing anything further.
That’s a good point. I’d avoid running maintenance tasks until the RAID state is clear. I’ve seen similar situations where the difficult part is deciding whether to replace the drive immediately, keep the array degraded for a while, or focus on getting the backup completed first. When there are several options with different risks, I usually write down the choices before acting. For example, if I’m stuck between two possible next steps, I might use a simple yes-or-no tool like decidal just to make the decision process clearer. It doesn’t replace checking the logs or following the ReadyNAS guidance, but it can help separate the decision from the technical troubleshooting. Once the replacement is installed, I’d monitor the resync closely and verify that the volume returns to a healthy state.
Prior to replacing or adding a drive you should ALWAYS first insure the backup is up to date. The RAID re-sync leaves the volume vulnerable to any secondary issue such as drive failure or anything that might be caused by a power outage too long for your UPS to handle. Drive failure is more likely during the re-sync because it puts more stress on the drives than normal usage. Drive failure on another drive is also more likely if they are the same age as one that already failed.
Balance won't do anything here, but also is pretty benign. The MDADM RAID and BTRFS are unaware of each other for a balance, so a degraded state doesn't matter. Still, no sense in doing it.
On an ReadyNAS, scrub starts both a BTRFS scrub and an MDADM re-sync, which should definitely be avoided on a degraded volume. No sense in triggering a re-sync that will not fix the issue but still puts the volume at risk only to have to do yet another re-sync later to actually fix the problem.
Replacing the drive will add no space, it will add a second layer of redundancy. RAID redundancy CAN save your data from failure, and RAID6 will do better at that that RAID5 ( which degraded RAID6 effectively is), but there are many types of failures that RAID cannot overcome. You should really think of RAID more for maintaining maximum AVAILABILITY than backup. That is, for many failure types, such as a single drive failure, you don't have to take the NAS offline to restore data from a backup.
Having lost one drive, that could mean your others are also approaching an age at which failure is more likely. It all depends on whether they were put in the NAS at the same time. RAID re-sync puts a lot of stress on the drives, so another could fail during the re-sync. But right now, you can lose another drive and not lose the volume. If you wait for another failure, you will lose the volume if yet anther fails during re-sync after you replace the second failed one.
If, after reading this, you still just want RAID5 instead of RAID6 and you want the "degraded" state to go away, see RAID6-to-RAID5-without-volume-re-creation-is-possible.
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