Multiple zpools

[Berdine]

Hi,

Having read the excellent guide written by Cyberjock about ZFS storage design and other FreeNAS information, some points about zpools are not totally clear to me. I would be very thankfull if you can enlighten me.

In an example in the guide (example 2), we have one zpool containing 2 vdev in RAID-Z2, each one made of 6 hard disk.
"This zpool provides redundancy against a maximum of 4 simultaneous hard disk failures(2 in each VDev), but not 3 in any one VDev." As I understand it, if 3 disks in any one vdev crash, the entire zpool is crashed : no data can be restored.

In all the examples of this guide, there is only one zpool. Can we have more than one zpool ? I do hope so, and as I understand it, we can.

So, is there any interest in this configuration, instead of having two zpools, each containing 1 vdev in RAID-Z2, each one of these vdev made of 6 hard disk?
The result would be the same ("These zpools provide redundancy against a maximum of 4 simultaneous hard disk failures(2 in each VDev), but not 3 in any one VDev."), but if 3 disks fail in any one vdev, the other zpool would not be crashed.

I clearly understand that it is only an example, but I am troubled by the fact that not any one example mention two zpools.

If I lack some understanding on this, I am afraid to make mistakes building my own NAS.
Indeed, I would like to have the following configuration :
- one zpool P1 containing one vdev V1 of 2 hard disks D1 and D2 in mirror mode, containing data.
- one zpool P2 containing one vdev V2 of 1 hard disk D3 in stripe mode, containing music and movies, for access for everyone at home, but with no need of redundancy.
- one zpool P3 containing one vdev V3 of 1 hard disk D4 in stripe mode, for storage for peer-to-peer, using transmission; no need of redundancy either.

This way, my data are reasonably safe, my medias always available, and my data server working, all in one.

In the future, I shall add another hard-disk D5 in the vdev V2 to make a mirror, if I want redundancy, but that is not my priority. I shall also add a spare hard disk, but for now, if any of the hard disk in V1 crash, I will replace it by D4.

Do you have any suggestion, or advice on some point I would have missed ?

Thank you by advance. And excuse me for my english, hope I have been clear.

 

[hugovsky]

As I understand zfs,

In an example in the guide (example 2), we have one zpool containing 2 vdev in RAID-Z2, each one made of 6 hard disk.
"This zpool provides redundancy against a maximum of 4 simultaneous hard disk failures(2 in each VDev), but not 3 in any one VDev." As I understand it, if 3 disks in any one vdev crash, the entire zpool is crashed : no data can be restored.

On first question about 1 zpool with 2 vdevs, you are correct.

If I lack some understanding on this, I am afraid to make mistakes building my own NAS.
Indeed, I would like to have the following configuration :
- one zpool P1 containing one vdev V1 of 2 hard disks D1 and D2 in mirror mode, containing data.
- one zpool P2 containing one vdev V2 of 1 hard disk D3 in stripe mode, containing music and movies, for access for everyone at home, but with no need of redundancy.
- one zpool P3 containing one vdev V3 of 1 hard disk D4 in stripe mode, for storage for peer-to-peer, using transmission; no need of redundancy either.

You are correct too. No need to ID diferent vdev across zpool. On zpool P1 you have vdev1. On zpool P2 you have vdev1. But that doesn't mean they're the same. (Just to explain it better).

Don't forget that if you value your data, ECC is a MUST. RAIDZ1 is dead. And always have backups!

 

[Berdine]

Thanks for your answer hogovsky.

I indeed have ECC memory, and have backups of my valuable data. ;)

 

[Robert Trevellyan]

In all the examples of this guide, there is only one zpool. Can we have more than one zpool ? I do hope so, and as I understand it, we can.

You can certainly have multiple pools. Multiple pools are more flexible, but less convenient. Your example requires managing space utilization on 3 pools. If it works for you, no problem, just recognize that there is a tradeoff.

 

[Darren Myers]

I'm currently managing 4 data sets on 3 pools of 7 hdds each. I find it more flexible to allocate specific datasets for certain data that i have, i also went and cataloged all my hdds by make,model,serial as well as what tray theyre located in; but i also added warranty status,expiration, purchase date, and included invoices.

 

[Berdine]

Robert and Darren, thank you both for yours answers.
I too prefer to have specific pools for specific data. The first pool contains valuable data which I can not lose, the second data for media center (movies and music), easily replaceable, and the third data for torrent server, easily replaceable too. These three pools are accessed diffently. The first is seldom accessed, by comparison with the two others. The second is accessed a few hours a day, mostly in the evening, while the third is always sharing data with the entire universe.
I expect disks in the first pool to last much longer than the ones in the third, the former being much less sollicited than the latter. And that is for the best: I do not mind replacing disks in the third pool often, while that operation for my valuable data is more risked.
Besides, space management in one pool is indeed an advantage, but in my case, I found it easier to have different pools. If my media center exceed a certain size, I know its time to delete some movies. If the pool containing my valuable data is overload, I know I have to buy new disks to extend it (even if I had not think of the way to do that yet).