fastest controller supported

[SweetAndLow]

Are these VMs running with their vmdk on the NAS? Or are you going to mount storage in your VMs?

The fastest drive layout is using several mirror vdevs in your system. Max out memory and possibly get a slot if you are using NFS and ESXi datastore on FreeNAS.

 

[Chris Moore]

need a 12 Gb/s controller for 6 - 8 8 TB Hitachi drives

The speed is the question. With the number of drives you have available, if you use RAID-z2 (two drives of redundancy, similar to RAID-6) it will limit the speed to the vicinity of 400 to 600 MB/s depending on the exact specs of the drives. If you use a pool of mirrors, it could be much faster, about 800 to 1000 MB/s and it still depends on the exact spec of the hard drive so it could be a little faster or slower than my estimate.
More disks would be needed if you need full 10GB speed and if you need high random IO, the mirrors are better. RAID-z2 is much better for sequential IO where high random IO is better handled by mirrors.
How fast do you need and what amount of storage do you need at the end?

 

[SweetAndLow]

The speed is the question. With the number of drives you have available, if you use RAID-z2 (two drives of redundancy, similar to RAID-6) it will limit the speed to the vicinity of 400 to 600 MB/s depending on the exact specs of the drives. If you use a pool of mirrors, it could be much faster, about 800 to 1000 MB/s and it still depends on the exact spec of the hard drive so it could be a little faster or slower than my estimate.
More disks would be needed if you need full 10GB speed and if you need high random IO, the mirrors are better. RAID-z2 is much better for sequential IO where high random IO is better handled by mirrors.
How fast do you need and what amount of storage do you need at the end?

Mirrors are more about iops than about streaming bandwidth. For every vdev you get the iops of a single drive. So more vdevs more iops.

 

[David Sheetz]

Are these VMs running with their vmdk on the NAS? Or are you going to mount storage in your VMs?

The fastest drive layout is using several mirror vdevs in your system. Max out memory and possibly get a slot if you are using NFS and ESXi datastore on FreeNAS.

We want the storage on FreeNAS just for backups, archive and templates so speed is not needed except mainly for write. Weekly this data will be copied off of the FreeNAS to removable drives and taken offsite.

 

[SweetAndLow]

we want the storage on Freenas just for backups, archive and templates so speed is not needed except mainly for write. Weekly this data will be copied off of the Freenas to removable drives and taken offsite.

Ahhh so you actually don't care about speed. RaidzZx performance will be plenty fast for your usage.

 

[Ericloewe]

1. add storage that can be common to all VM hosts I have (some are in vcenter and some are standalone free esxi) common ground is they can all use and iSCSI mapping.

No problem, that's what ZFS does best.

As others have said, if you're just backing up the virtual disk images, RAIDZ(2 is probably most appropriate) performance should be acceptable.