A little confused over mirroring

[kaigoh]

Hi.

This week, I've been lucky(?!) enough that, despite two drive failures in my ZFS pool, I'm managing to save most of the data. I've brought a couple of 8Tb drives and am about half way through copying my data over to the new drives.

To save anything embarrassing in future, I want to make the pool more redundant. All the research I am doing suggests that mirroring is better than RAIDing, certainly in a home environment.

However, despite my research, I am still confused on a couple of points.

What I want to do is this:

5 * 3Tb HDDs in a VDEV mirrored to 2 * 8Tb HDDs in a seperate VDEV, all in one pool. Where I am getting confused is, it seems that in posts such as this one (https://dawning.ca/2017/freenas-11-add-a-drive-to-create-a-mirrored-zfs-volume/), the instructions seem to be mirroring disks in a one-to-one relationship, rather than mirroring across VDEVs?

Is my plan possible, or would I be better off just having two pools and syncing the data between them? Maybe via snapshots?

Thanks,

Kai

 

[BigDave]

Slideshow explaining VDev, zpool, ZIL and L2ARC for noobs!
This resource will explain the basics and will answer your questions.

 

[jgreco]

Mirroring works at a device level. See the link @BigDave just put out.

You could set up a separate pool and rsync your data to it, which seems to be the sort of protection you are envisioning. This is nearly as good as having two separate NAS boxes and syncing between them, except that you're still dependent on the single physical box.

 

[Ericloewe]

All the research I am doing suggests that mirroring is better than RAIDing, certainly in a home environment.

No. There are advantages and disadvantages.

 

[danb35]

the instructions seem to be mirroring disks in a one-to-one relationship, rather than mirroring across VDEVs?

Yes, that's how mirrors work. You mirror disks, not vdevs. All redundancy happens in the vdev. When you have more than one vdev, they're always striped together.

All the research I am doing suggests that mirroring is better than RAIDing, certainly in a home environment.

Would "all the research" be largely based on this blog post? Although he makes some good points, I think he overstates his case, both with respect to "don't be greedy" (since when is it "greedy" to want to maximize your storage utilization?) and to the oh-so-horrible stress on the rest of the pool when resilvering RAIDZn (which happens to be exactly the same stress as when you're doing a scrub, which you should be doing regularly anyway).

 

[kaigoh]

Yes, that's how mirrors work. You mirror disks, not vdevs. All redundancy happens in the vdev. When you have more than one vdev, they're always striped together.

Thanks, that is pretty much clear now

Would "all the research" be largely based on this blog post?

That was definitely one article I read. I can see where he is coming from, and certainly if I was in a mission-critical environment where data was more of a concern than money, then the options I am considering would be different. But the content I am backing up is not end of the world if I lose it type stuff, so meh, I think the snapshot backup idea I have is a goer for my needs.

Thanks for the reply's though, much appreciated.

Kai