Noob advice needed - expansion of drives and choices

Hi all - new to NAS world so please bear with me, need a bit of a sense check to make sure I understand how the below could work.

I have 6x 12tb HDDs in a gaming rig (only 3 currently have data I need to keep - 3 can be wiped). Aim to shift to a 8 bay NAS but do not plan on filling out the extra 2 bays right away (probably a couple of years away) but want the option to add 2 drives later on.

If I go the TrueNAS route I’m confused on how to set this all up and am hesitating just to use windows with storage spaces (but I hear that’s crap so prefer not to). The data stored isn’t critical so I don’t feel uncomfortable with a raidz1 format (important data is bascked up externally anyway).

Going TrueNAS how would I do this most effectively?

  • Would I have to create a 4 drive vdev then leave out my 2 spare drives until I can buy another 2 to make another 4 drive vdev to add to the pool? (a shame as it means I can’t use 2 of my drives for now)

  • Could I create a 6 drive vdev then add the extra 2 drives in a mirrored vdev to the pool? Would this create issues for the overall pool on drive failure? If this is possible, could I use 2 hdds that are the same size as each other but different sizes to those in the 6 drive vdev?

  • Is there another better way of doing this? Should I be looking at another software solution?

Thanks and sorry for the basic question but I’m having trouble wrapping my head around this.


Take it the other way around.

First: What are your storage needs? Are there different tiers of data (possibly different pools), or is it just a big bulk of data (one pool, but quite possibly different datasets for different purposes)?

Then what are your requirements for security/resiliency and flexibility?
Resiliency is better with raidz2/raidz3. Flexibility, and IOPS performance, is better with mirrors but 2-way mirrors of large drives are somewhat less secure than raidz2/3 and 3-way mirrors are expensive.

With 8 bays your options are:

  • Single 6-8-wide raidz2 (or raidz3 if you’re paranoid). Secure; most space efficient. You need the drives right now.
  • 4-wide raidz2. Secure; can start with one now and add a second vdev later but does it have enough capacity righ now?
  • Up to two 3-way mirrors. Safe and ready to migrate right now, but no obvious use of the last two bays; probably not enough capacity.
  • 2-way mirrors. Flexible now and for future expansion, but not the most secure.
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I’ll just leave that here



You can. It feels weird, but it is feasible. It will be ugly to look at, but it/s supposed to work.

This doesn’t sound like it will work with your plan. You have, in pragmatic terms, three disks to start off with, so a 6-wide RAIDZ1 is out of the question. You can buy more disks now or do something like a pool of two-way mirrors, for crappy space efficiency but lots of flexibility.


Just to make sure, these disks are not SMR… are they?

Alternative solution is Unraid, which is proprietary and requires purchasing. Not a fan, but a lot of people like it because it allows for easy expansion. You choose how many parity disks you want, then you can continue to add drives as long as they are smaller than the parity disk(s).

People who really care about their data use ZFS though.


Thanks all. Will read the whitepaper in more detail too.

So basically I’m limited to a max 3 drive vdev if I don’t want to lose the data on the existing drives? I guess I can lose that data, won’t be too much of an issue really, if a 6 drive Raidz1/2 + a 2 drive mirror is the better way to go. Overall prefer not to do a 2 way mirror as it’s pretty expensive

No idea if SMR or not and can’t seem to find an easy way of finding out with a Google search - they are WD Reds as far as I can remember.

As I say, the data isn’t really critical, so maybe I could just run the HDDs in sequence so if one fails I just lose everything on that drive and not what is on the others (then no point using ZFS I guess…)

WD Reds are a red (pun intended) flag regarding SMR, make sure to check since SMR (especially WD’s) is not compatible with ZFS. List of WD CMR and SMR hard drives (HDD) – NAS Compares

There are still points in using ZFS (ie snapshots), but overall if you don’t care for your data just keep using your windows system since it’s cheaper.

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I’m thinking the best overall would be to have your six disks in three sets of two-way mirrors, striped together, leaving two bays open to add another pair in the future. This would also simplify getting the data that’s currently on three of the disks, onto the NAS:

  • Create the pool with three disks, striped.
  • Copy the data from one of the remaining disks onto the NAS
  • When complete, add that disk as a mirror to one of the striped disks in the NAS
  • Repeat the last two steps for the remaining two disks

All of this can be done in the GUI, but until you get the third disk added as a mirror, your data is vulnerable to failure of one disk if the wrong one fails.

Another option depends on how soon you might need those last two disks. RAIDZ expansion is supposed to become available in TrueNAS SCALE by the end of this year, though probably not in the GUI until some time next year. If you don’t expect to need the extra space until next year or later, you could create a 6-disk RAIDZ2 vdev and plan to expand it later with another disk or two. The risk here is that this feature is delayed again.


Thanks for the link - lucky me, they are all CMR it seems. Was aiming to set up the NAS to avoid letting the gaming rig run 24/7 (200w power draw ends up being a lot) rather than planning for guaranteed safety of all data

I thought SMR was only a factor for <= 8 TB disks, so they shouldn’t be.

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Thanks, this sounds interesting, especially as I don’t realistically plan to add the last two extra drives before 2025.

Would prefer not to go the mirroring route for all of the drives as it’s a bit of a hit for the overall budget/storage space. The 6 drive raidz2 + waiting for expansion abilities might be the way to go (will lose my current data but oh well such is life).

Another point is that, while we generally love ZFS and TrueNAS here, it isn’t for everyone, and many people find it has kind of a steep learning curve. If data integrity isn’t super-important to you, you may want to look into other NAS software. OpenMediaVault seems to get pretty good reviews, and it’s free software just like TrueNAS.

Not in the least trying to talk you out of TrueNAS, but there are options.


Thanks a lot everyone - really helpful answers and has saved me a lot of headaches. I think OMV with a Raid 5 array may be enough for my needs and seems to allow for both saving the data on my 3 drives and transfering to the NAS + adding 2 extra drives down the line.

Much appriciated

You could create a degraded 4-wide raidz2 with your three drives (double degrade 5-wide raidz2 even?), transfer your data to it, and then complete the vdev with the disk(s) you’ve transferred data from. But it’s a bit risky.
For raidz# layouts, ZFS really requires buying all drives upfront.

To say the least.

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If you are happy with 50% parity (like 4-way RaidZ2), mirrors is a good way to go.

Most performant in many ways, most flexible.

You pay for that with 50% parity.

No more than 3-way RaidZ1

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…or a (temporary) stripe of 3 drives.

No. Less risky. There could be 1 disk or redundancy in a degraded raidz2