Help me configure RAIDZ1 with 3 drives

[tording99z28]

I have 3 8TB drives that I want to configure RaidZ1 with. In the GUI with the volume manager how do I do this? I have tried different options for disks and mirror and stripe and it won't let me do any of them. Can someone tell me how? I have read the ZFS primer and the Storage area of the FreeNAS guide and they are not helping much. Thanks in advance.

 

[dlavigne]

Post a screenshot of what you are seeing when you try to select the 3 drives.

 

[tording99z28]

I don't know if this is right. BTW this is not with the 8TB drives yet, I am doing a test with smaller drives just to make sure I know how to set it up when I get my third 8 TB drive.

 

[dlavigne]

Click the X to remove that second bar of drives. You can then drag all 3 drives in the top bar. This assumes that you are making a pool for the first time (that is, you don't already have a volume of just one drive).

 

[tording99z28]

Click the X to remove that second bar of drives. You can then drag all 3 drives in the top bar. This assumes that you are making a pool for the first time (that is, you don't already have a volume of just one drive).

What drop down option do I select then? Mirror or Stripe? I was reading and I thought this would give me 2x read speed and redundancy for one failed drive?

 

[dlavigne]

As long as you have 2 bars, it thinks you are making 2 vdevs.

You want all of your disks to appear in one bar. That way you can drag the slider to select all 3, at which point RAIDZ1 becomes an option in the drop-down menu.

 

[tording99z28]

As long as you have 2 bars, it thinks you are making 2 vdevs.

You want all of your disks to appear in one bar. That way you can drag the slider to select all 3, at which point RAIDZ1 becomes an option in the drop-down menu.

Ah okay I got it, I didn't realize it gave you another option in the drop down. So what if I add a 4th drive and want to do RaidZ2 would I then have 2 vdevs of 2 drives with RaidZ as the dropdown option or would I leave all 4 drives in one vdev with the RaidZ dropdown option?

 

[danb35]

I leave all 4 drives in one vdev with the RaidZ dropdown option?

You'd put all four drives in one vdev with RAIDZ2 chosen in the dropdown. It only appears if you have at least four drives.

 

[wblock]

Two vdevs of two drives would normally be two mirrors striped together. This is often known as RAID10, although ZFS calls it "striped mirrors".

Some obligatory warnings:

It is not possible to add a drive to a RAIDZ1 to make it a RAIDZ2. After the vdev is created, the only way to change it is to back up the data elsewhere, destroy the volume, and then create the new one.

RAIDZ1 is not recommended for large drives like this. The problem is that it takes a long time to resilver big drives, and the odds of a second drive failing while the first is being replaced are too high. And if two out of three drives fail in a RAIDZ1, the volume is lost. The size limit for RAIDZ1 should be three 4TB drives. Many here in the forums recommend no more than three 1TB drives in RAIDZ1. Some also say that LZ4 compression changes those numbers, but it only means that the size limit is fuzzy, it's still there. RAIDZ2 gives two drives of redundancy, so even if a second drive fails while the first is being replaced, the pool is still working and data is not lost.

 

[tording99z28]

Thanks for the info and warnings guys. For now I will have to run with 3 drives in RAIDZ1 and then when I have another drive in my budget back it up and destroy it and rebuild the volume for RAIDZ2. When you say it takes a long time to resilver a big drive like this what do you consider a long time? More than a few days?

 

[wblock]

It varies depending on the system. Some can take days, yes. One very nice thing about ZFS is that since it knows which blocks are occupied, it only needs to copy those. Hardware RAID copies the whole drive every time, since it has no way of knowing which blocks actually contain data.