Raidz2 configuration for optimal 12 drives pool?

[Daisuke]

I have a new Dell R720xd setup with 12 x 8TB drives controlled by a H710 mini flashed to IT mode. TrueNAS Scale runs on a separate SSD.

I want to obtain the maximum amount of space for a Raidz2 setup, I currently get approximately 65TB total and I was expecting to see at least 75TB:

What is the optimal Raidz2 setup for my disks? Using 2 vdevs will make me lose 4 disks instead of 2, not sure what to do.

Thank you for your help.

 

[sretalla]

At 12 wide, you're getting very close to the maximum (of 16... https://openzfs.github.io/openzfs-docs/Performance and Tuning/Workload Tuning.html#pool-geometry-1) recommended by the OpenZFS project and your rebuild times will be terribly long.

If you accept that, then 12 can technically happen.

In order to understand where your data is going (and remembering that there's TiB and TB to think about as different counts of the real storage capacity), you're probably best to use the RAIDZ calculator here: https://wintelguy.com/zfs-calc.pl

It's probably worth looking up the actual GB rating of the disks you're using vs GiB to ensure you enter the right size in the calculator.

 

[Daisuke]

Thank you, I appreciate the useful details. I’m using 12 HGST Ultrastar He8 Helium (HUH728080ALE601) drives, purchased on multiple batches, from different sellers. With two on the shelf for surprise failures. What size should I enter into calculator, 8000?

 

[sretalla]

What size should I enter into calculator, 8000?

That seems mostly right... it would be great if HDD manufacturers were clear about their units on the box though... they often use units interchangebly (in their favor).

 

[sretalla]

Also be aware that you'll be running at the IOPS capability of only one single disk (although your throughput may get somewhere closer to 6 disks), which may mean around 2-300 IOPS in total for the pool.

OK if you're just serving large files, but will perform very badly for block storage or VMs and won't be great for lots of small files either.

You seem to have fixated on RAIDZ2, so I assumed you know what you're doing, but just wanted to be clear (perhaps for others who might read this).

 

[Daisuke]

The default pool of 12 disks is used for storage of large files, archive type used read only. Anything related to services or VMs will run on a mirror1 pair of 1TB SSDs with TRIM enabled, called services pool. To give you an idea, I will use less than 10GB for running services and probably never use VMs. Any thoughts on additional settings to be implemented for default tank? I left everything default installation settings.