Hot Spare vs. Cold Spare

[Logikgear]

So I'm gearing up to add more drives to my server and redo my RaidZ to a RaidZ2 but I'm unsure how I want to go about doing my spare drive. My plan is to do a 6 drive RaidZ2 with 4TB drives and having one Spare. I'm not sure if I want to have a hot spare or a cold spare. What does everyone think of the difference. My HBA is Hot-Swap capable and I am using an 8 Bay chassis. So I have the drive bay space.

I like the idea of having a hot spare ready to go so the system can fault out the failed drive and resliver the new one in automatically. My concern is unused drive life. I'm using NAS rated drives. 4 WD Reds and 3 HGTS Ultrastar Enterprise drives. If I don't have a drive failure for years then I have one drive (my hot spare) will have been sitting there spinning for years. I can't find any statistics on Hard drive spindle wear over years so I'm unsure.

So what say you on Hot Spare vs. Cold Spare?

 

[anmnz]

Just putting all 7 disks in RAIDZ3 up front seems smarter to me than RAIDZ2 + hot spare. Why wait until you have a problem before adding that disk to your vdev?

And although a cold spare isn't spinning, also it's not being scrubbed, it's not running smart tests, and it's burning through its warranty period just as fast.

So my answer would be "neither". :)

 

[Stux]

I run out and buy a replacement drive on or near the day that the last one failed...

 

[Arwen]

Another option is a warm spare. Spinning and ready for replacement by using the GUI. Until then, you can use it as a single disk pool for local backups.

The concept of using RAID-Z3 instead is a good one for reliability for the pool. But, that does nothing for backups. (Out of box, or offsite backups would be better for disasters, but many restores are from user errors.)

I do like having a free slot for replacements. That helps replace-in-place, a safer method than pulling a disk and using that slot for the replacement.

 

[nojohnny101]

I don't think hot spares make much sense unless you at going to be away from your box for long periods of times (weeks, months) and you need absolute 24/7 uptime.

You already have good redundancy (but as others have said, not a backup) with radiz2 and the likelihood of losing 3 drives before being able to replace one is extremely low.

I personally follow @Stux logic and I just wait until one dies or shows signs of dying then I go out an buy a replacement. My priorities and needs of my NAS doesn't require it to be operational 24/7 nor am I away from my box for more than a week. If things really go south, I just shut it down until I can deal with it.

In the end you have to sketch out your priorities and then pick a strategy that fits that and your budget.

 

[Logikgear]

Thank you everyone for all the awesome suggestions. I'm going to go with anmnz's idea of the 7 drive RaidZ3 which will give me one blank Drive Bay for when one dies and I can swap in the replacement.

Something I forgot to mention is I do have backups. I have an on-site backup server that backs up the important data and I have off site cloud backup which is a mirror of the backup server.

I'm never away from my NAS more than a couple of days and I can pick up a replacement drive either locally or from Amazon with two day shipping.

 

[anmnz]

To be honest although I do think RAIDZ3 is a better plan than RAIDZ2 plus a spare, I wonder if it's overkill. If your backup and replacement strategies are sound, isn't RAIDZ2 enough?

(Of course that is a question about your own judgement and appetite for risk and so on, and nobody can answer it for you. It's an observation not a criticism.)

Having a spare drive bay is a very good idea, I think!

 

[Stux]

To be honest although I do think RAIDZ3 is a better plan than RAIDZ2 plus a spare, I wonder if it's overkill. If your backup and replacement strategies are sound, isn't RAIDZ2 enough?

(Of course that is a question about your own judgement and appetite for risk and so on, and nobody can answer it for you. It's an observation not a criticism.)

Having a spare drive bay is a very good idea, I think!

Maybe the 7-drive RaidZ2 and enjoy the extra space ;)

 

[Arwen]

Hot spares make more sense when you have 2 pools and can share the spare between them. Then RAID-Z2 with HS over RAID-Z3 and no HS.