For this issue, have you come across raid
bitmaps?
No, I hadn't.
Glad to be of service.
With a setup that does both of those, RAIDs would be much less painful.
Ah, there's more...
I proposed something years back that seems to be making it's way through Neils list:
When a drive is about to fail, insert a new hot spare, fast mirror from the failing drive to the new drive and only look at the rest of the RAID for parity when a bad block is encountered. Meanwhile all new writes go to the transient mirror.
This speeds up resync/restore for a failed drive massively and you essentially only rely on RAID resilience for the few failing blocks, not all the Tb of data.
Finally, put a RAID 1 SSD bcache in front of a RAID6 backend (with working barriers... one day...) and I think that becomes a very, very fast and reliable system.
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