If you suffer a drive failure, your odds of a successful rebuild onto 
that spare are decidedly mixed.

https://marc.info/?l=linux-raid&m=139050322510249&w=2

On 9/12/22 04:06, Wols Lists wrote:

On 12/09/2022 01:58, Phil Turmel wrote:

quoted

Hi Wol,

On 9/11/22 06:08, Wols Lists wrote:

[trim /]

quoted

old one is still good I'd go for a 3-disk raid-5 plus spare. That's 
my current setup.

Eww.  Don't do that.  Always convert raid5+spare to raid6.

At the moment the fourth drive is, in my mind, a transient backup. I 
don't want to make it an actual part of the array in case I want to 
remove it.

I'm thinking of getting a second matching drive, but seeing as I've 
bought 16TB of drive space in the recentish past, another 8TB seems 
excessive :-)

Cheers,
Wol