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I've heard numerous times that installing an OS on a USB key is a bad thing to do, as USBs typically have a certain number of writes before dying, and installing an OS on it will wear it out (unless it's used sporadically for rescue purposes).

Nonetheless, I am very tempted to install some flavour of Linux (Ubuntu or Arch, I haven't decided yet) on a small, transportable, USB Key. My problem is, although you read a lot that it's "bad", you are never told how bad. How long would it last (provided, say, a pc that is 24/7 on)? A month? A year? Five years? Is there recipes to make it last longer? Is there any reason beside weariness that should prevent me from attempting this?
I mean, if it can be calculated, then I could theoretically shield myself by doing regular backups on another key when the deadline gets close (for example).

Notes

  • I am not talking of using a USB as a live CD, but actually installing the OS on it.)
  • When I say "USB Key", I refer to the little USBs with a flash memory, not an external USB hard drive.

For the curious, my reason is that I work in a lot of different places, on different PCs, and I have a very customized session, with my own WM, my own key bindings, my own scripts, , a selection of plugins for firefox and chrome, etc, and currently I am synchronizing all this through a mix of dropbox, git, and transporting files on USBs, and and it's becoming a chore. It would be much simpler for me to just plug the USB and mount the hard disk of the PC I am using and use it's processing power without actually needing to install any OS on it.

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closed as not constructive by DragonLord, Xavierjazz, Nifle, Mokubai, Sathya Apr 13 '12 at 4:09

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Newer usb keys typically have a bigger number of writes before dying. So that depends on chosebn key. –  blogger Apr 11 '12 at 17:05

2 Answers 2

Flash memory degrades because bits are stored by trapping electrons on a gate, requiring strong electric fields that wear out the material inside the cells. As the material wears, it becomes more difficult to transfer electrons to and from the gate, but different drives have different thresholds as to when a block is considered a failure. They also have varying amounts of spare blocks to use when one fails and may use different wear leveling techniques. As the amount of wear per write cycle is very unreliable to begin with, there is no clear rule of how long a usb drive should last.

Creating regular backups is a solid plan, but there is no increased need to do so when you suspect your drive is failing. Reading the contents of a block does not involve the damaging high voltages and the device will be reporting write errors to your OS long before the contents become unreadable.

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If you make it readonly and mount heavy-writing partitions such as /tmp to tmpfs, and log to a central log server, then usb can last a long time, often years. make them as close to livecd as possible.

However, to my surprise, the usb quality varies greatly, even from the same (supposedly reputable) manufacturer! One batch would run for over a year with no issues, and another has 1/2 of them fail within a few weeks.

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by the way, i used ubuntu and / mounted on error remount readonly. since if you have sufficient memory the os will be cached in memory so you should be fine when it gets to the readonly state which requires a reboot. i discard the usb when it happens a few times, or when the initial fsck found errors. usb keys are good for replicating disposable os installations that are substantially the same, ideally even the differences such as network settings come from a dhcp server. –  johnshen64 Apr 11 '12 at 18:32

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