Issue Replacing Disks | RN316 automatically shut down instead of rebuilding RAID array

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Platypus69 wrote:

 

Not sure really why it should take longer to rebuild/resync the RAID as I add each disk. I would have thought that it would be roughly the same, as each time you have to read the other 5 x 4TB worth of stripes to calulate the missing stripe. And then expand the volume after the final HDD is synced. (There will be no data modifications during this entire process.)

 

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The volume expansion isn't deferred until the end.  It will begin with the second disk insertion.   BTW, you likely will need to reboot after the second disk syncs - and make sure the volume is fully expanded before you proceed to the third disk. 

So the first disk replacement requires 24 TB of disk i/o.  The last one will require 60 TB of disk i/o.  The time goes up simply because the volume is getting bigger as you proceed.  The total process will need 264 TB of i/o to complete. 

A factory reset would have built the volume once - requiring 60 TB of disk i/o, and another ~24 TB to restore the data.  So it would have taken approximately 30% of the time (assuming you already had an up-to-date backup).  You could have also used RAID-6 - many people prefer the extra protection with very large volumes.

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Platypus69 wrote:

nd might foce a scrub after each one, just to be sure.

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Don't do that - the RAID scrub will just double the i/o (and the time).  Then there would be a BTRFS filesystem scrub on top of that.  

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Platypus69 wrote:

Surely the alert is for the use case when you are not present and cannot replace the HDD relatively quickly, in which case you would argue that you shut down the NAS as another HDD could fail mathematically (so higher risk, than shutting them down and hoping they come up and are OK.)

Likely that is the use case.  Of course a disk failure can look like a removal, so I understand why the timer would start then.  However, the insertion should cancel it.