TrueNAS Mirror multiple vDevs

Hi Folks
I am starting my journey on creating a TrueNAS server using an old PC ( Intel i7-4770K / Haswell Z87 Chipset). Finished with the install and in the process of setting it up.

I intend to configure 8 disks in a RAID10 configuration. I choose RAID10 instead of the popular parity based RAIDS for the following reasons

  • My hardware is old and i dont want to put a lot off stress on the CPU/Motherboard. My understanding is that any parity based RAID config will put a lot of load on the CPU.
  • I am using non ECC RAM so the lesser computation and calculation the better.
  • Rebuilding a failed parity based RAID puts a lot more stress on the remaining disks of the raid compared to the RAID10.
  • I understand that from a reliability point of view RAIDZ2 is better that RAID10 but given that i also have physical backups i am ok with risk of have the option to loose only one disk.

Now comes my query. Since i have 8 disks should i configure the Pool with 4 vdevs (mirror) of 2 disks each or 2 vdevs(Mirror) of 4 disk each ?

One pro of going with 4 vdevs is faster read/write performance. Not sure if there are any drawbacks of going with 4 vdevs of 2 disks ?

Your views ?

It’s not that stressful on the CPU putting them all in one pool, this post further breaks down all the concepts.

For me I usually want the most storage so I put them all in one pool and it’s using a slower CPU than you are.

Your hardware may indeed be a bit old, but especially the CPU is more than capapable for RAIDZ2. My new FreeNAS box (built in October 2020) actually uses a 4 core Xeon E5 1620, which is probably older than your i7. And it usually idles at no more than 15% utilization. The biggest peak I have seen so far was around 50%. And before that I had RAIDZ2 on an AMD Phenom 4 core.

I don’t want to convert you over, but the hardware age is certainly not a good reason for avoiding RAIDZ2.

For reference: A scrub on my RAIDZ2 (8 x 16 TB Seagate Exos) takes a bit less than 5 hours.

Thanks a lot Tom.
To begin with let me tell of a “DuH” moment i had. I am your youtube channel subscriber and watch you videos often. In your video you frequently mention that you will leave the links below and i search for the links below in the youtube video description and i dont find them. Initially i thought maybe you will add them later. But then I never could find them. When this happened too often… i realized i was probably doing something wrong and for the life of me i could not figure out what. Then i joined the forum and then realized that for each video you post on youtube there is a thread created in the forum and then the tubelight in my head flickered and finally switched on…the links you talk about below are in your forum thread below the video post. Now that i think about it should have been obvious given that you put the forum thread link in the youtube video description and most of your followers would be coming from the forum and not directly on youtube… Anyways the Duh moment has passed and now i am a bit more wiser :slight_smile:

Coming back to the topic on hand… Thanks a lot for the links. A lot of things just go cleared up

1 - 2 Vdevs of 4 disks each in mirror config actually creates 4 copies of the same data (a 4 way mirror). I thought it would divide the storage in half like a normal RAID1. So if i want to use RAID10 with 8 disks i will have to create 4 vdevs of 2 disks each.
2 - I totally misunderstood IOPS and Streamed Read/Write. Now i understand that where more users are accessing the NAS, IOPS becomes very important compared to streamed read/write speeds. Where there are very few users accessing the NAS, IOPS is not that important compared to streamed read/write speeds

Given that i have very few users 2-3 users and that this will be used primarily for backup and for storing the media library and based on the links you shared i am now thinking of using either 2 Vdevs of 4 disks each with RAIDZ2 or 1 vdev of 8 Disks with RAIDZ3. Based on the performance test in the links The 2 Vdevs provide higher performance compared to the single RAIDZ3 Vdev, but it will take a total of 4 disks for parity compared to the 3 in the single Vdev. But iam confused on this.

Also from the links did not realize that compression (LZ4) could give such a performance boost. So is it worth enabling compression ?

Thanks Chris for this. I was not considering RAIDZ only because i thought my CPU could not handle it. But now given that the concern is ill founded, i am going ahead with RAIDZ. The only thing to decide is 2 RAIDZ2 (of 4 disks each) or one RAIDZ3 of 8 disks?

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Related to the links, I mostly have them at the bottom of the video description but I have also been adding them as a pinned comment as people don;t always expand the video description.