Risk management: choosing Z1 vs. Z2

[SoonerLater]

I have just ordered an ixSystems Mini-XL+. It has eight hot-swap 3.5" drive bays (plus a few 2.5" bays). It was my original thought to configure it as a 5-drive Z2 pool using 4 TB drives. With three empty drive bays to start with, I would have room to expand the original pool or add another when I run low on storage (which won't be for many years). I only use this for media storage for a family. I don't run any jails. It's just SMB shares.

But then I started thinking... maybe the thing to do is to build a 4-drive Z1 pool and have a hot-spare (or a shelf spare). I configure my existing server to notify me if a drive starts to die. Since this is a hot-swap system, as long as I have a spare, it's very likely I could replace a failing drive very quickly so could probably live with Z1 level of redundancy (as opposed to the Z2 I've used for years). And going this route, I could have another Z1 4-drive pool in the future. Two years from now, at least 6 TB and maybe even 8 TB or 10 TB drives will be as cheap as 4 TB are now, probably. Except for needing backup to a different destination / host (ideally cloud based), this Mini-XL+ could satisfy my needs for a decade.

Thoughts?

 

[jgreco]

It's a super-bad idea to have your redundancy sitting there useless.

If you lose an entire drive in a RAIDZ1 vdev, you lose redundancy, which means that any additional unreadable data, such as a bad disk sector, is unrecoverable. ZFS allows you to add a second disk to get RAIDZ2, which gives you redundancy to cover such a case, or RAIDZ3, to cover an even more catastrophic scenario.

 

[Samuel Tai]

I would counsel Z2 over Z1 in pretty much all scenarios. The forum is full of folks whose Z1 pools are dead because the probability of 2 drives going out is much higher than you would think. Also, if for some reason you're away for an extended period (holidays, vacation, etc.), and aren't physically available to react to a down drive, then you'll have no redundancy until you return.

 

[SoonerLater]

In the eight years that I've been using FreeNAS / TrueNAS, I've only ever used only Z2 pools. But because I've been running them on on low grade (and even lower grade) hardware, I was foolishly thinking that I would be sufficiently risk-tolerant merely by running a Z1 pool on the Full Monty of a hot-swapable genuine iXSystems-built system.

OK... I'm sober now. Back to reality.

 

[jgreco]

Yeah, it's not the server you have to worry about, as much as the drives.