Thank you very much for your post.
At work I manage allmost one petabyte of data. Used raid solution is based on traditional raid (raid-4-DP). The file system is striped over multiple raid arrays.
This allows use of large file systems. Each raid array can deal with losing 2 data drives simultaniously before a raid array would go down. Hot spares are a must here.
Thank you for your explaination about Unraid and how it works. I could not have put that in better writing.
I am a little worried that I have not been able to find the right words to get the message over.
Personally I have no doubt in Unraids raid and file system concept. I feel Unraid is doing a splendit job!
Double parity based array together with mirrored cache is a good enough solution in most cases.
In general has data protection different protection levels. Parity is one, double parity is another one, Mirroring is one and backup is also an important one.
Hypothetical speaking in regard to the risk for multi disk failure:
It might seem over the top at first but when automatic assignment of a hot spare is possible in case a disk has died on you one would save time and by that reduce the chance for a multi disk failure even further.
Not even considering a scenario where a replacement disk is not available and still needs to be purchased before this disk can be added to the array.
Hope that I was able to defend my hot spare opinion this time.
Regards,
Marcel