Previously, I had 15 10TB drives in my NAS, consisting of 2x RAID-Z3 pools with 7 drives each, and 1x hot spare shared between the two.
I recently snagged a deal on another 10 TB HDD, so I can either:
Add it as a second hot spare, shared between the two pools, or
Take the two unallocated drives and grow each pool by 1, leaving me with 0 hot spares
I’m aware that it is not yet possible to expand an existing vdev by just plopping a new drive in, but I have enough free space that I could shift files around, scrap one pool, re-add it with 8 drives, then move everything over and repeat on the other one.
So my question is: how unwise is it to run with no hot spare when dealing with a pool of this size? All of my drives are used, and I probably won’t get another hot spare until another good deal pops up, however long that takes.
A drive runs fine until it doesn’t. No one can make better estimates
I wouldn’t worry about spares that much with a 7-wide Z3 setup. It’s very resilient. Even if you lose a drive in a vdev, you still have two drives left and 7-wide Z2 isn’t a critical state. Unless you’re on vacation for 4 weeks and can’t react to drive failure, I don’t see a problem.
But the pool will run in degraded mode and performance will be lower.
And look at it this way: if you’re down a drive, even a less favorable HDD deal suddenly becomes way more appealing
But if you’re the guy doing 4+3 RAIDZ config anyway…I think you can sleep better with a spare slotted and active.
I’d personally change the 4+3 setup to 5+2 and keep the spare or run with two spares. More capacity and a spare ready to do it’s job. RaidZ2 means that you have to lose 3 drives in a vdev for unrecoverable data loss. 3 drives out of 7 is a lot.
