Unfortunately, there’s no really clear answer to that question. To be honest, I don’t how much Ubuntu is writing to the installed drive, though my guess is probably not a lot. As long as you’re not memory constrained on the machine that you’re using it on, there’s a good chance that it’s mostly reading. When you become memory constrained, Ubuntu may fire up a paging file, which could cause a lot of write activity. But my guess is that Ubuntu itself isn’t doing a whole lot of writing.
I am a bit concerned about the flash drive, but it actually makes sense. Let me explain.
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The brief life of flash drives
The problem with flash drives is that companies use inexpensive materials to make the flash memory, so they wear out over time. This isn’t like a Solid State Drive (SSD) which uses a higher quality flash memory that actually lasts longer than most computers are expected to last.
Unfortunately, exactly how quickly they wear out is just impossible to say. It depends on exactly how much Ubuntu is writing to the disk – and even if it’s not a lot, it depends on the quality of the flash drive that you have. So there’s no way to really predict.
In a situation like that, the solution is fairly simple. Back it up.
Backing up your flash drive
Take that flash drive and do an image backup, a full backup, or whatever kind of backup makes sense for you and save it to a hard disk.The flash drive wearing out is a when-not-if situation, so when it does wear out, you can get a new one and put the backup image back onto this new device. Then, you’ll be up and running just fine.
How often you back up depends on how painful the loss would be. If the drive suddenly failed and you lost everything since the last backup, how far back would you want the backup image be?
Why a flash drive works in this case
But I want to be clear. I really like the idea of having Ubuntu installed on a USB device that you can basically plug in almost anywhere and just have it work. You have your own operating system on pretty much any computer to which you have access to the USB port and that will actually allow you to reboot from the USB. I think that’s a pretty neat thing.
I also think that using cheap flash drives is exactly the right thing to do for this. There’s no reason to spend a lot of money for this as long as you back it up. Once you’ve got it backed up then, then I think you can use this for a long time. You may go through a few flash drives as they wear out and that’s okay. The backups are going to save you from having this be a real problem.