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Are there any circumstances under which the SD card can be removed from the device while powered up?

Perhaps it could be possible to operate only from RAM temporarily? This could allow a different SD card to be plugged in to copy some data to RAM or to the web before plugging the original card back in.

If it's currently not possible, could it be done with some careful software changes?

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As @fredden stated it is not safe. The easiest method would be to attach a card reader to the USB port. You can find these for for around a dollar on ebay. –  Steve Robillard Nov 28 '12 at 5:19
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3 Answers 3

up vote 6 down vote accepted

Well, it's not safe if any filesystem present on SD card is mounted (especially if it's root filesystem that is mounted). This is true by default in most distributions currently available for RaspberryPi. But it is not strictly needed. You can run your system from RAM (either by copying filesystem image to tmpfs mounted filesystem or by using initramfs) or some external harddrive or even from network. If you do so, your SD card can be swapped without problems (just ensure to unmount all filesystems mounted on it).

The only problem is that RaspberryPi has small amount of RAM so you plan on running it this way, you should have really small image (compressed filesystems like SquashFS may be handy here), memory split that gives ARM most RAM and probably 512MB version of RaspberryPi. But that's definitely possible.

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As far as I know, it's not safe to remove the disk (SD card, Hard Disk Drive, etc) the operating system is running on while live.

You may like to look into UnionFS, combined with a RAM disk. Linux Live CDs run predominately out of RAM, but I'm not sure how much might be needed in your case.

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While SD cards are electrically safe to remove from the RaspberryPI, the bootloader, and root filesystem are currently mounted there, so without some major changes, it isn't safe to remove the SD card while powered up.

If you need to read another SD card, you can attach a USB based card reader to read from other cards, as drivers for external storage should be present

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It would be useful to differentiate between safety in terms of electrical hotplugging, and safety in terms of integrity of mounted/relied upon filesystems. –  Chris Stratton Nov 29 '12 at 21:42
    
I added those changes –  Marshall Anschutz Nov 30 '12 at 17:05
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