Background:

My primary interest in using internal boot drive for my Unraid server is for redundancy. Decreasing boot speed is a distant second.

Even though I believe my motherboard supports TPM 2.0, I don't think I want to tie the Unraid license to my motherboard.

Since I am using both of my motherboard M.2 slots for cache drives, and I don't really have any slots to mount SSDs, I am thinking that using two USB thumb drives in a mirrored internal boot drive setup might be my best option.

I am currently running Unraid 7.3.1, but will be upgrading to 7.3.2 early next month.

Questions:

• Once I setup the internal boot drive(s), my existing USB thumb drive will no longer be valid to use in Unraid. I could, however, utilize it for any other purpose, correct?

• In the future, if one of the USB thumb drives failed, Unraid would seamless switch to the other drive and notify me that the other drive has failed, correct?

• If I am not using TPM and I need to switch motherboards (hardware upgrade or failure), I could just plug one or both USB thumb drives into the new motherboard (along with all of the array and cache drives) and be up and running, correct?

• If I head down this path, I am planning on purchasing two 64GB INNODISK LYTX DVR-70 drives (per the Unraid Boot Device Guide). The drives are USB 3.0; should I be plugging them into USB 2.0 or USB 3.0 slots on the motherboard?

• Also, my understanding is that Unraid will create a 32GB BTRFS partition, with the remainder of the drive(s) formatted as ZFS. Is that correct?

Since you don't want to use fTPM, your license needs to remain on a USB drive.

When you migrate to internal boot the two Innodisk drives handle the boot function -- but the license anchor stays on a separate USB drive that must remain permanently connected.

So your actual configuration will be three USB drives total -- two Innodisk drives in the mirrored boot pool plus your existing USB drive repurposed as a dedicated license anchor.

On hardware portability -- when you move to new hardware you'll need to bring all three USB drives along with your array and cache drives.

The license travels with the dedicated USB license drive, not with the boot pool drives.

Worth considering an alternative -- a discrete dTPM module for your motherboard's TPM header (if available) typically costs $10-20 and eliminates the third USB drive requirement entirely while avoiding the fTPM vulnerabilities the guide covers.

If your motherboard has a physical TPM header this is worth looking at before committing to the three USB drive approach but your future migration would be restricted by the TPM header availability on the new machine.

Now to your specific questions:

The mirror continues operating on the surviving drive after a failure and Unraid notifies you.

Be aware of a documented in an NVMe configuration bug in 7.3.1 where replacing the failed mirror member can leave a stale device entry requiring a terminal zpool detach command to clean up. Supposedly fixed by now.

For port selection -- USB 2.0 ports for all three drives. USB 3.x drives in USB 3.x ports generate more heat.

Use your motherboard's internal USB 2.0 headers with 9-pin adapter cables.

On the partition structure -- the boot partition is ZFS not BTRFS.

8GB minimum -- sufficient for boot but it's up to you which size to select. The remainder becomes the data partition if you choose to use it.

The Innodisk drives are the right choice for this application -- but make sure you account for the third drive in your planning before purchasing.

One final note: the mirrored USB boot pool is the least utilized and tested configuration among all available Unraid boot options.

Real world deployments are rare and documented cases even rarer.

I've documented it in the guide based on JorgeB's confirmation that it's supported, but I don't use this configuration myself and can't speak from personal experience.

Proceed with that context in mind and make sure you have solid backups of your config folder before attempting the migration.

One more thought on the redundancy goal specifically -- it's worth stepping back and evaluating whether the additional complexity of this setup is justified for your situation.

A mirrored boot pool protects against a single drive failure.

But Unraid's config folder backup -- which you should be maintaining regardless of boot configuration -- already provides recovery from a complete boot drive failure in minutes.

The question is whether the seamless failover of a mirror justifies three USB drives, the barely tested configuration complexity, and the migration process compared to simply maintaining a current config backup and keeping a spare USB drive on hand.

For some use cases the mirror makes sense.

For others the simpler answer is a quality boot drive with a current backup.

Worth thinking through before committing

Edited yesterday at 06:38 AM1 day by Lolight

Thank you, Lolight, for taking the time to respond with such complete information. Based on your reply, using a mirrored USB internal boot pool without TPM or fTPM would still leave me with a single failure point: the dedicated USB license anchor. So that's really not a good option, not really any better than a single USB boot drive.

So based on your information, I plan to stick with the single USB boot drive. I do backup the flash drive weekly (I assume that's what you mean when you mentioned the Unraid config folder backup), and I have a script set up to automatically rsync those backups to my QNAP NAS.

Would the Innodisk USB drives still be a good choice for a single boot drive setup? I have been using a 32GB Sandisk (Planar TLC) for over a decade without any issues, but it sounds like it would be a good idea to replace that drive with something better. I'll make sure to pick up an identical spare drive as well.

From what I can tell, using a USB drive larger than 32GB is supported these days by the Unraid USB Flash Creator.

Exactly right on all counts -- you've worked through the logic correctly.

The Innodisk drives are an excellent choice for a single boot drive setup.

The same specifications that make them good for a mirror make them ideal as a single drive.

A single Innodisk running Unraid will likely outlast everything else in the system.

Buying an identical spare is exactly the right approach.

On capacity -- yes, Unraid Flash Creator supports drives larger than 32GB now. 64GB is fine.

But if you encounter any problems with formatting use Rufus first.

Out of curiosity -- how did you confirm the Planar TLC on the SanDisk?

Standard tools like ChipGenius or Flash Drive Info Extractor can't read SanDisk controller data since they lock out NAND identification.

Wondering if you have a source for that specific model's internals.

I googled "sandisk cruzer fit 32gb planar tlc" and it returned this: The SanDisk Cruzer Fit 32GB is an ultra-compact, low-profile USB 2.0 drive optimized for permanent plug-and-stay usage in car stereos, TVs, and laptops. Regarding its NAND technology, it uses cost-effective planar (2D) TLC memory, prioritizing space-saving portability over high-speed read/write performance.

Conversely, when I googled "sandisk cruzer fit 32gb 3d tlc" it returned this: The SanDisk Cruzer Fit 32GB is an ultra-compact USB 2.0 flash drive intended for "plug-and-stay" storage in tight spaces (like car audio or smart TVs). It does not utilize 3D TLC NAND; it is a legacy USB 2.0 drive built on older, lower-cost controller architectures.

I guess there's a possibility that google is wrong...