BTRFS read-only state, OS 6.8.10, ReadyNAS Ultra 4

I agree with Sandshark that you should back up the NAS before doing anything else.

Also, I agree that rebooting a NAS with a read-only volume is dangerous.  You are lucky that it remounted.

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ziemowit wrote:

I have 4 x 2TB disks in my ReadyNAS and all but one are of the same type (3 x ST32000542AS + 1 x ST2000DL003-9VT166). All have same rotational speed.

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When the time comes to replace disks, I suggest you go with Seagate Ironwolf or WD Red Plus.  Avoid the WD Reds, as they are SMR.  Most desktop drives between 2-6 TB are also SMR.

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ziemowit wrote:

 

 

Questions

• I want to understand what is going on. Which boils down to:
  • what logs should I read?
  • what am I looking for in the logs?

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Generally I start with dmesg.  Look for disk and btrfs errors, also look at the mdadm commands. 

Looking at the bottom of volume.log can help you sort out if you have a full OS partition (md0)

Readnasd.log and status.log are often useful in sorting out the history of degraded volumes

systemd-journal.log, system.log and kernel.log, mdstat.log often have useful clues as well.

Of course you also need to figure out what to do about what you are seeing.

If you like, you can upload the log zip to cloud storage (dropbox, google drive, etc) and send me a PM (private message) with a link.  Make sure the link permissions are set so anyone can download.  You'd send a PM using the envelope icon in the upper right of the forum page.

It might take a while (over a week) for me to get back to you, as I'm going on vacation soon and won't have much time to spend on this.

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ziemowit wrote:

I want to prevent future problems with similar issues.

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If you have no backup plan in place for your NAS, then that is the place to begin.  RAID isn't enough to keep your data safe.  The best way to do that is to have at least one copy on another device (and ideally one copy off-site).

One thing to do is set up a maintenance schedule on the volume settings page.  I run one of the four functions (scrub, balance, disk test, defrag) every month.  The scrub and the disk test will access every sector of every disk, so both can give early indications of disk issues.  I space those test two months apart (filling the gaps with the balance and defrag).

Don't rely on the web ui to give accurate information on disk health.  Often there are clear issues in the log zip that don't show up in the web ui.  So it is wise to look at the log zip from time to time - particularly after each scrub and disk test completes.

Make sure you maintain at least 15% free space on the volume. If you use snapshots, I also suggest turning off the smart snapshots and switching to custom settings.  Set an explicit retention period, and also configure them to only make snapshots when there are changes.  This can help manage the amount of space the snapshots take up.

I also suggest getting a UPS for the NAS.  That will ensure it shuts down cleanly when there is a power outage.  A lot of volume failures involve unclean shutdowns.

If you run the antivirus software, the file search feature, or have apps installed on your NAS, then you should also consider upgrading the RAM to 4 GB.  Generally removing apps and disabling services you don't need is a good idea - improving both performance and stability.  Antivirus and file search in particular use a lot of system resources.