USB-Stick for booting OS - risk analysis

TrueNAS General
1

Hi everyone!

I fully understand, that using USB stick for the operating system is not a good idea due to high risk of unpredictable failure.

BUT: what if I have a cloned usb stick readily available, fully configured and tested to work, if swapped out?

(Further, I have the config stored somewhere else, so I could even create a new installation in a breeze.)

So the real question is: what could possibly happen to my zraid1 data, when the OS crashes due to a defect USB stick? Real Data loss on writes?

I’m looking forward to your thoughts!

regards
Mike

2

Do NOT use a USB flash stick in normal production running. Period.

In an emergency, for a short period, a USB Flash stick can be used but it could fail pretty quickly due to the number of writes.

However you can get a genuine SSD in a USB Stick format (e.g. SKK - which I use) - and these have much much much higher TBW for used as a boot drive. There are other potential issues with using USB for a boot drive, but at least you have avoided the TBW drive dying issue.

A RAIDZ1 pool shouldn’t have any problems coming back after a system crash (for whatever reason - failed USB stick, power outage whatever) but:

  1. That is only true if you have set up your hardware correctly; and
  2. “Shouldn’t have problems” is not the same as “never have problems”.

Implement @joeschmuck’s Multi-Report script to (amongst many other benefits) have your system configuration file mailed to you once per week as a backup.

3

THAT.
Your pre-made “cloned” stick will get out of sync pretty quickly.

But preferably do not use a UDB stick to boot, although nothing bad should happen to your data pool.

Cost analysis question: How many sticks should one burn before it gets cheaper to use a $10 SSD behind an USB adapter?

4

I wouldn’t encourage the idea, but (as long as you aren’t using encryption) there shouldn’t be any risk to your data. I don’t know that I’d trust a clone of the boot device, but “boot a fresh install and upload the saved config” would get you back up and running in a hurry.

What I’ve done instead in the Microserver I handle is use an internal USB-NVMe adapter with a 2242 (I think) SSD. There’s an internal USB port on the motherboard for just this purpose.

5

Im using a small 60gb SSD attached to an USB SATA adapter for boot, without issue. Total cost from AliExpress 7€ for both (5€ SSD and 2€ the adapter).
Don’t wanna say that Is the best choice, but imo risks are less than benefit, so its worth (1 SATA port free, as 1 power connector from PSU… So i could build a 6 disk raidz2 pool without HBA).
A good MLC USB stick (for me) cost 3 times more, and probably Is less reliable; the pci-ex/NVME adapter Is a very better choice, just a bit more expensive but way more reliable.
My mainboard have an internal dedicated USB port, so i could secure the device to the case avoiding accidentally “impacts”

1 Like
6

guys, thanks for all that feedback!
I’m also thinking about an eSATA-to-SATA Adapter for 10 Bucks, since the Micorserver offers such a port on the back… power is coming via USB, so I could easily run any 2,5" SSD… or spinning drive… since I have such an old baby lying around…

7

Here are some issues I have experienced with my USB SSD:

  1. USB disconnects - less frequent on some ports than on others i.e. USB2 is probably more reliable than USB3.

  2. USB → SATA bridge doesn’t support TRIM.

I suspect that eSATA is probably more reliable than USB.

8

Just use two. You can select two to install too, or add a second later in the boot pool menu to make a mirrored boot disk.

Then run daily or weekly scrubs, set up multi-report script to receive a mailed config.

You will have virtually no chance of crashing due to a corrupted boot pool, but a reboot may fail until you pull the now dead USB.

The two issues with thumb drives are that:

  1. they generally have poor endurance, and due to the amount of boot pool writes made these days tend to get burnt up pretty quick.

  2. they generally have poor performance, leading to a laggy interface and experience.

These issues are worked around when you use an m.2 or sata to USB adapter to use a higher quality boot medium.

9

Depending on the hardware, the power supply might also become an issue.

For example, the internal USB port of the HP ProLiant Gen8 with Intel CPUs, is only a USB 2.0 port, thus supplying 2,5W max. *

Kingston lists the max draw of a SSD at 3,2W while writing. Add to that an USB to SATA converter and TN writing a lot of logs, I would be worried hat in the long run, this might damage the USB port.

*Maype HP has beefed this up so any device connected can draw more power, I have read in the past that some mainboards manufacturers have done this, but who who knows.