Comment by cm2187
11 hours ago
For home usage, if you have backups raidz1 is fine (just do an incremental backup at the first sign of trouble). If you don’t have backups, then you probably shouldn’t be running a NAS in the first place.
11 hours ago
For home usage, if you have backups raidz1 is fine (just do an incremental backup at the first sign of trouble). If you don’t have backups, then you probably shouldn’t be running a NAS in the first place.
The risk of z1 is that if you get a read error during resilvering, that data is permanently corrupted. The odds of this happening go way up the larger your individual drives are. This is why I chose RAIDZ2 for my NAS. I've had to resilver 2-3 times over the past 10 years, and never lost a byte of data.
> The odds of this happening go way up the larger your individual drives are.
This is a common claim, but honestly, citation needed.
We can't just apply bit error rates from the datasheet that haven't been updated in 15 years. I'm sure a 2-day rebuild is a little more risky than a 4-hour rebuild, but I'm not convinced it's by all that much. Especially if you had a monthly scrub going to prevent disk rot and disks secretly getting super fragile.
> I've had to resilver 2-3 times over the past 10 years, and never lost a byte of data.
And how many times did you have a read error on one of your other disks during a resilver?
In the Linux ISO community the math is different because none of the data is essential, however there is a lot of it. Backing it all up even one time to an off-site location would be a 2x expense for a hobby. So 3-2-1 is hard to justify.
Instead the math can be different e.g. it's ok to lose some data but not all. Therefore you might prefer the unraid approach over zfs where losing more than parity doesn't kill the whole pool.
I'm actually in this boat right now. I have 2x26TB drives in a 4 base nas (two empty, plus 3x M2 empty) and I'm trying to decide the best way to set them up. I have around 3TB of backups that I care about as backups (but they don't need to be online, just archive backups at this point), and around 5TB of media that can be replaced.
I don't want to lose 26TB just for a mirror, and I have a spare 8TB USB HDD. I'm torn between unraid and just Debian, and I'm torn between just two separate devices and one RAID 1 partition one RAID 0
For most people snapshots are enough backup. It is still useful to have an offsite backup, but realistically fire is rare enough that you can risk it, and that is about the only risk most people have (you can have your NAS in a location likely far from where a fire might break out to reduce the risk farther).
Fire, malware, accidental deletions, capricious RAID controller (pre-ZFS). And that’s only the stuff that happened to me. Add power surge, theft, correlation in SSD failures (eg power on counter overflow firmware bug), damaging the array while moving, etc.
Malware, accidental deletion, RAID controller issues - all things ZFS with snapshots are immune to. You can decide if the other worry you or not - the risk is not zero, but it may be acceptable. Your backups are all subject to similar issues.
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This isn’t black and white. You might have huge amounts of non-essential data that aren’t worth the cost of off-site backups, but worth the cost of an extra disk of redundancy to lessen the risk. Even when you do have backups, it will reduce the risk of extended downtime (and possibly egress costs) caused by having to restore large amounts of data from backups.
The middle ground I go with is to structure the pool using datasets and zvols, and then periodically backup the critical ones using zfs send. For example, I can live without my movie collection, but I cannot afford to lose personal photos.