Build and disk layout question

[SteveKB]

I'm relatively new to TrueNAS, but not storage in general...but ZFS might be throwing me for a loop:
I have a NETGEAR ReadyNAS104 that is getting full (and old) that has 4x8TB (RAID5) drives for a total of ~18TB. I want to build up a TrueNAS system and move to some grownup storage. My initial plan was to buy 4 more 8TB drives, set them up on TrueNAS, migrate my data from the NETGEAR, and then move the 4 "emptied" drives over to the TrueNAS setup to make one big happy share. However, looking at how ZFS works, I think I need to revise my plan and was wondering if someone could sanity check it. Here's what I was thinking (and questions I had):

1. Create new pool on TrueNAS (pool1)
2. Add 4x8TB new drives as a RAIDZ1 vdev (vdev1) to the new pool (This would result in a ~24TB pool?)
3. Migrate data from the NETGEAR to pool1
4. Pull the unused drives from the NETGEAR and put them into TrueNAS as a second RAIDZ1 vdev (vdev2) under pool1.
5. Total size of pool1 would be about ~48TB?

Would this setup be risky? Would there be a better way to do this (larger "new" drives)?

 

[NugentS]

RAIDZ1 on large drives is considered unsafe due to the resilver times. I suggest RAID Z2. That would be 16TB in the first vdev with another 16 in the second. Note that data will NOT be balanced between the vdevs in this scenario which means you won't get the mild speed advantages of two vdevs. (new data will go to the second vdev until the vdevs are approx 50:50

Note that balancing existing data into another vdev involves a lot of reading and writing

 

[SteveKB]

RAIDZ1 on large drives is considered unsafe due to the resilver times. I suggest RAID Z2. That would be 16TB in the first vdev with another 16 in the second. Note that data will NOT be balanced between the vdevs in this scenario which means you won't get the mild speed advantages of two vdevs. (new data will go to the second vdev until the vdevs are approx 50:50

Note that balancing existing data into another vdev involves a lot of reading and writing

So maybe the more efficient answer is to offload the ReadyNAS into a pair of external USB drives and then build my ZFS pool with 8x8TB as RAIDZ2? That theoretically should give me ~48TB and give me some breathing room if I have to resilver? The data is just video, so not super critical, just large and can be offline for a while.
Also, in theory, that would allow me to replace failed drives with larger ones, so once they all die I could resize the vdev accordingly?

 

[NugentS]

Yup. As long as you don't expect too many IOPS from the single Z2 vdev you should be fine

 

[SteveKB]

Yup. As long as you don't expect too many IOPS from the single Z2 vdev you should be fine

How dismal IOPS wise? I'd just be streaming video...

 

[Ericloewe]

Single disk’s worth. Not great, but fine for sequential workloads like video.

 

[NugentS]

As @Ericloewe says. A single disk of IOPS. RAIDZ is OK at sequential workloads, which is exactly what streaming video is