Quick check - *temporary* pool & dataset on a USB thumb drive?

TrueNAS General
1

Hello all

I want to plug a 128GB Sandisk USB “thumb drive” into my TrueNAS box, create a new pool (“temp” or something) which uses all of it and then, via a TrueNAS “app”, write transient (days, maybe a week) data to a dataset therein whilst also deleting some of it to keeep it from filling up.

I’m currently doing it as part of my existing pool, having created a quota limited dataset on it, but I can’t manage it fast enough without it filling up.

Using a USB drive might enable me to manage the datset more rapidly, but anyway I can unplug it now and then and delete it or even erase it before using it again (with the attendant unmounting of the pool which I am yet to read about).

Is there anything inherently disastrous about this “thumb drive” approach in terms of jeopardising my other pools (4 HDDs in a ZRAID2 configuration) or upsetting TrueNAS in some way?

[edit: spelling mistakes]

2

So long as you do NOT include this thumb drive as part of an existing pool and create a pool of its own, then it shouldn’t jeopardise your other pools.

However:

  • Flash drives have a much more limited write lifetime (Total Bytes Written) than an SSD - so you might want to think about using e.g. an SSK USB SSD (looks like a flash drive but is an SSD instead)
  • USB connections are not as reliable as SATA or SAS, so you may get occasional disconnections, and when this happens your pool goes offline (but because it is ZFS it will be fine when you bring it back online).
3

Excellent: this is what I was hoping to read and the ZFS nature being tolerant of disconnections isn’t something I knew about. very good reasurrance - thanks.

I understand the limits of USB thumb drive flash devices and their connections not being properly reliable but in this case, the data’s ephemeral and it’s just me messing about with some ideas so I don’t mind if it goes wrong.

Interestingly (well, I think it is interesting!) I have just found and ordered a 32 GB Sandisk (Western Digital) uSD card which is specified to 1920TBW* (!). My TN installation has an uSD card slot on its motherboard; I’m intending to try it as the boot pool, just for the fun of experimenting (I have read in the forum about the likely problems of flash wear and speed but in this case it’s an industrial card and it was cheap - £15 - so worth a try).

It would free up a SATA allocation for other experimenting as described here. But now, I think I could consider the uSD card as my “temporary pool” if it being a boot device doesn’t suit me.

But the main thing is it oughtn’t to mess up the existing storage - thanks @Protopia

(*In comparison, the Crucial (Micron) SSD I am using solely for my boot-pool is specified for something in the region of 320 TBW from memory).

4

ZFS is NOT tollerant of USB disconnects - your pool will likely go offline and stay offline until either a reboot or a physical removal / re-insertion of the drive + possibly a manual action to bring it online.

5

I understand. I was rather referring to this

It seems like it’s robust enough for my purposes and I agree, USB is not desiged to be a high reliability interface.

6

People do use USB pools as local backup targets

It’s not really reliable enough for continuous pool usage, but as a manual backup destination it seems to work.

7

Nice - it’ll be a good way for me to test a couple of ideas until I work out a better, longer-term solution (which is currently merely a fledgling notion).

Luckily the data is ephemeral - merely jpegs and video clips from me playing around with an NVR - so a relatively unreliable USB destination will suffice for now.