using a striped pair in a zpool?

[travalon]

I have just gone over cyberjocks incredible guide 3 times in a row, paying particular attention to the examples of zpools. I understand more and more every time I read it. But, I still don't know if it is possible to stripe 2 2tb drives into a 4tb vdev and add it to 3 4tb drives in a raid z2. The adding vdevs section of the guide leads me to believe it is possible. I do understand it is probably a very bad idea for all the reasons i've read in the manual and guide, however I will be buying some new drives this month and would like to maximize what I have. (Currently 2 2tb mirrored) As soon as possible I will replace the striped vdev with a true 4tb drive and use the 2 2tbs (mirrored again) for a OwnCloud setup in a jail. NO i do not have any of the recommended hardware. The only thing the gurus may approve of is 24gb ram though its not ecc. I do understand the risks/issues i may encounter but I can afford to lose my data. It would suck but, it has now been consumed and re-purposed into tools to help me learn. Once I've got it figured out then I'll invest in better hardware.
SO, is possible to stripe 2 2tb drives into a 4tb vdev and add it to 3 4tb drives in a raid z2?

I have to use:
i3-2100
asrock Z77 micro-atx mobo w 8 native sata ports 32 gb max ram
24 gb ram - 2 x 8gb & 2 x 4gb
2 x 2tb WD red
Trying to decide which drives to get 3tb or 4tb x 3 or 4 drives
running freenas fron 8gb usb3.0 or possibly a class 10 - 4gb sd card
corsair 430W cx v.2 PSU

Not sure If I'll use the following: (or for what)
1 corsair 120 gb ssd
1 sandisk 32 gb readycache ssd
May pick up an intel gigabit nic

Thanks

 

[joeschmuck]

To answer your question,"Don't Do It!". You need to read cyberjocks information again, you missed a huge part. If either one of those new drives fail, all your data goes bye bye.

Also, you didn't specify if you're using ECC RAM and MB. If these are already in your possession and have to use them, so be it but you are hopefully aware of the risks.

 

[danb35]

But, I still don't know if it is possible to stripe 2 2tb drives into a 4tb vdev and add it to 3 4tb drives in a raid z2.

No, it is not possible, because it is not possible to have three disks in a RAIDZ2 configuration. You can have four (or more) disks in a RAIDZ2, or three (or more) in RAIDZ1. But assuming you meant three disks in RAIDZ1, yes, it is possible. It will also mean that if either of the striped disks fails, your entire pool will fail, which is the main reason it isn't a good idea. The second problem is that once you've added that striped vdev, you can't remove it. So your plan of "As soon as possible I will replace the striped vdev with a true 4tb drive and use the 2 2tbs (mirrored again) for a OwnCloud setup in a jail" isn't going to work, unless you're planning to destroy and rebuild your pool in the process.

 

[Ericloewe]

You cannot make vdevs out of vdevs. That does not work. Vdevs must be made up of drives.

 

[travalon]

Ok thanks. I like to do the unconventional. My idea was to use 2 x 2tb striped + 3 x 4tb in a Z2 config. It looks like I'll have to go for the 3TB drives as they are cheaper and use them in a z2 using 1 of the 2tb +3 x 3tb. I know until I upgraed the 2tb to a 3 I won't get the full storage of the other 3 drives but my question has been answered and I usually bow to superior knowledge/experience. Thank you all for answering my question.

 

[Ericloewe]

Ok thanks. I like to do the unconventional. My idea was to use 2 x 2tb striped + 3 x 4tb in a Z2 config. It looks like I'll have to go for the 3TB drives as they are cheaper and use them in a z2 using 1 of the 2tb +3 x 3tb. I know until I upgraed the 2tb to a 3 I won't get the full storage of the other 3 drives but my question has been answered and I usually bow to superior knowledge/experience. Thank you all for answering my question.

To be more accurate, it would be possible to have such a setup, but it would be a hack behind ZFS' back and thus a typically bad idea.