Should I buy a cold spare now or later?

[Ginger Penguin]

Hi all,

 

I'm planning an overhaul of my NAS at the moment and my current thoughts are 5x8TB HDDs in Raidz1. Should I get a spare now so I can swap it in if a drive fails or is it generally considered to not be worth it and to only get the spare when it's needed? Nothing on the NAS is going to be mission critical or anything. It's mostly a Plex server and a backup of past video projects. I've heard recommendations of getting them later due to warranty expiration and the fact that prices will likely be cheaper in a few years when a drive failure is more likely than now.

 

Thoughts?

[RONOTHAN##]

Depends on your tolerance for down-time. If your system isn't mission critical and you're able to shut down the server for 2-3 days while you wait for a new HDD to arrive so the drives aren't running before starting the rebuild or you live next to somewhere where you can buy one on a moments notice (say a Micro Center or Best Buy), I wouldn't really worry about it. If the system needs the nine nines of uptime (which it doesn't sound like you do), then I would probably have 2 on hand, though if that was the case you'd probably be running the drives in RAIDz2 instead. 

[OhioYJ]

I've also gone back and forth on this and eventually decided against having a spare just sitting around. One I can order a drive at any time and have it shipped to me typically in a day or two. So getting a new drive fairly quickly isn't really a big deal. Second, what happens if here in a couple years I decide to redo my NAS and use larger drives? I guess I could leave the smaller drives in there, but not as likely, then my spare is just another unused drive I need to do something with.

[Ginger Penguin]

2 hours ago, RONOTHAN## said:

you're able to shut down the server for 2-3 days while you wait for a new HDD to arrive...or you live next to somewhere where you can buy one on a moments notice

Yeah, I don't have too much of a problem with that. I would prefer to be able to have my Plex server still going but I'm aware that would be very much wishful thinking! And I don't live that close to anything like that but there are places I could easily drive that aren't too far away. I might have to replace it with a different model at that point though. Who knows what manufacturers will be making a few years from now? I may be wrong in this but I recall that the drives don't have to be identical but you can't replace a drive with one of a smaller capacity to the others, is that right?

2 hours ago, OhioYJ said:

what happens if here in a couple years I decide to redo my NAS and use larger drives? I guess I could leave the smaller drives in there, but not as likely, then my spare is just another unused drive I need to do something with.

That's a really good point I hadn't considered. I can fit 8-10 drives into my NAS so I've left myself room for expansion but I would definitely imagine that if I do another storage overhaul, I would be swapping out for higher capacity drives anyway. Seems like the better idea is to wait until I need it.

[RONOTHAN##]

1 minute ago, W.D. Stevens said:

I may be wrong in this but I recall that the drives don't have to be identical but you can't replace a drive with one of a smaller capacity to the others, is that right?

That's right, identical is preferred, but as long as the capacity is the same or larger it's fine. 

[LIGISTX]

On 6/19/2022 at 9:26 PM, W.D. Stevens said:

That's a really good point I hadn't considered. I can fit 8-10 drives into my NAS so I've left myself room for expansion but I would definitely imagine that if I do another storage overhaul, I would be swapping out for higher capacity drives anyway. Seems like the better idea is to wait until I need it.

 Buy the “cold spare” and use it for Z2, don’t actually use it as a spare. z2 is a much better idea since the chances of a drive dying during a resilver is not small, it’s actually somewhat statistically significant in drives that large because of how long it takes to rebuild. RAID Z1 really is “dead”. 
 

But also, just remember, adding storage space to ZFS after the fact is not easy or cheap, you need to build a full new vdev with its own redundancy. So if you ever plan on needing more space, build out the widest vdev you can which seems like 10 drives for you. Definitely use z2 in a 10 wide vdev…. But the reason for this is because if you do say 6 drives now in z2, you will only be able to add a 4 drive wide vdev later, which is not very useful even if you only did a z1, which again, just isn’t super safe. 
 

I have had a second drive go offline while doing a resilver on my z2 array….. I was very thankful I had z2 and not z1. 

[Jarsky]

If you can afford and connect 6 drives, then RAIDZ2 will give you considerably better redundancy than a single redundant array. 

The downside to having a cold spare lying around, if you havent done some rigorous testing on it when you get it, it could be out of warranty by the time you need it. You also may never need it before its time for an upgrade. If something happens to it later and it has issues, then it could be a big waste of $$$. 

The upside is obviously you want your array degraded for as little time as possible, and having it on hand you can start a rebuild straight away. 

Another thing to consider is that 8TB drives are currently about $40 more than they are during sale periods, so you might want to wait until a sale to get the last one to save some $$$ on it. 

 

e.g my drives were $128 each when I got them, theyre currently about $180 each because of price inflation and not currently on special.