How do I add a new VDev without risking the failure of another VDev?

[avpullano]

Cyberjock's presentation on VDevs, zpools, etc. (stickied in these forums, for those who have not had the pleasure of reading it) states that within a given zpool, the failure of any VDev results in the failure of the whole zpool. I don't completely understand why this is true, but I'm starting to put the pieces together as I read more about zfs. Cyberjock also states that zpools and volumes are the same thing. Therefore, I would think that creating 2 volumes on my FreeNAS machine, each with a single VDev, would ensure that that failure of one VDev will not result in the failure of the other VDev.

However, this guide (http://www.allanjude.com/bsd/zfs-zfs.html) distinguishes volumes from zpools, stating that volumes are more akin to datasets. So which is true?

The point of this:I have a functioning RAID1 array and I would like to add new HDDs completely separate from this array. I do not want the failure of either array to affect the other.

 

[cyberjock]

Ok, "array" means nothing to ZFS. If you say "array" we're going to think you are talking about a hardware RAID array. And we're going to point you to the manual that says not to do that in about a dozen places and then leave you to deal with your own problems. So don't use that again unless that's what you want. ;)

Ok, don't confuse the zfs terms either.. there's volume, zpool, and zvol. zvol is NOT a Volume the way we talk about it. If you go to create a pool in FreeNAS you do it from the Volume Manager(because a zpool is considered a volume). If you want to create a zvol, you do it from a different place. zvols are basically like datasets but they are block storage instead of file storage. If you really want to get silly with the depth of knowledge, a zpool is not that much more than what you could call 'the master dataset' or equivalent. It is more, but not a whole lot more for you as the end user.

What I said in my guide is correct. A failure of any vdev in a pool will result in a failure of that pool. If you have 2 pools, each with one vdev, and you lose one vdev you will lose that pool and only that pool because of the underlined word. Pools are separate and distinct from each other and a failure of one has no bearing on the other unless they share a common failed hardware component. Vdevs in a given pool on the other hand are forever attached at the hip and if one goes over the cliff they all go over.

 

[avpullano]

Ahh, that clears up everything! The word "volume" gets thrown around in so many different places, I had no idea that "volume" and "zvol" existed as 2 completely different things. So when I create a new volume via the FreeNAS GUI, I will be creating a new zpool, which will have nothing to do with my existing zpool (except for any shared hardware, of course). Got it.

Thanks for the clarification, cyberjock. You are the "Spirit Admin" that we all try to channel while attempting to understand technical concepts. Much appreciated.