If you compare security only, not performance and capacity...

[Mark St.]

If you compare security only, not performance and capacity and as long as you have a file system like ZFS which does checksums:

a 2 drive mirror is a safe as a RaidZ1?
a triple mirror is as safe as a RaidZ2?

maybe even a little bit more secure because of the reduced complexity?

 

[Borja Marcos]

If you are considering a pool with a single vdev, in terms of resilience against broken drives yes, it's the same.

A 2-way mirror can survive the loss of a drive. A 3-drive raidz can survive the loss of one drive as well.

A 3-way mirror will survive the loss of two drives, the same as a raidz2 (which has a minimum number of four drives).

However, if you compare a 4 drive raidz2 to two 2-way mirror vdevs and you take Murphy's laws into account, the two-way mirror is less safe. It can survive the loss of two drives depending on which drives fail. As a worst case you might lose the two members of a mirror vdev.

 

[Heracles]

a 2 drive mirror is a safe as a RaidZ1?

Nope.

a triple mirror is as safe as a RaidZ2?

Neither.

The reason why a Raid-Z1 is not as safe as a mirror is because it relies on multiple disks to be free of any error when it is time to rebuild. A mirror need only a single disk to be error-free for a proper re-silvering.

As for the triple mirror vs Raid-Z2, the same logic applies : A Raid-Z2 with a single failed drive will still have redundancy to detect and fix an error. But in case there is more than one error to be fixed at the same time, it will not be able to do so. With 2 full copies from a 3-way mirror, the probability to survive multiple errors is much higher.

 

[Borja Marcos]

And yes, @Heracles, you are right as well, I was considering all or nothing drive loss.

 

[Mark St.]

So, for a single person with about 1 TB of office-documents (word, pdf, pictures), i go for 2 or 3 way mirror...not Raid.
Which means a small Synology-NAS (with btrfs which uses checksums) would be okay too

 

[Borja Marcos]

So, for a single person with about 1 TB of office-documents (word, pdf, pictures), i go for 2 or 3 way mirror...not Raid.
Which means a small Synology-NAS (with btrfs which uses checksums) would be okay too

I trust FreeNAS better thanks to ZFS.

Snapshot performance is second to none, you can afford the luxury of doing hourly snapshots. I'm not sure about other filesystems. And it't not just checkpoint-thing as "it supports snapshots" but their impact on performance, etc.

 

[Heracles]

I do not know their products but they surely have something that will fit your needs. What is important is not to forget about backups. No single server, FreeNAS / TrueNAS or Synology, mirror or Raid-Zx, can be more than a single point of failure. Plan your backups and test them by trying to do a restore.

 

[danb35]

Mirrors are a good choice for lots of smaller installations--I don't agree completely with this article, but it gives some good things to think about:

ZFS: You should use mirror vdevs, not RAIDZ. – JRS Systems: the blog

And you're right, mirrors on btrfs aren't nearly as broken as parity RAID is. Still not as robust of a filesystem, but it's an application that's not as likely to break.

 

[Borja Marcos]

Several years ago I had a nasty incident with a ZFS server. A defective HBA creating some random block corruption scattered all over the disks.

No data was damaged at all, it managed to survive until we noticed and we replaced the HBA. It kept correcting data blocks. I wonder how many filesystems can survive a defective HBA.

 

[Mark St.]

Ok, at this point i think it will be a Synology DS220+ (2x 2TB NAS, btrfs-checksum-Mirror) + 2 or 3 backup drives + cloud sync
A triple mirror would almost double the cost because there are no 3bay-variants.
i have no experience in building sff-systems so a 16x16x22 cm case is really nice.

thx for helping me with this "is a 2 drives mirror with checksums ok" thing......after nearly 3 months lockdown, mostly homeoffice, 3 kids at home and no sport...my own brain feels....degraded (and i am pretty sure this is not only a feeling)