I am going to guess that you have heard about the persistent overlay that Fedora 8*, 9, and 10 supports on a USB flash drive.
*Fedora 8 does not support persistent overlay but can still be installed on a flash drive.
So what is “persistent overlay“?
The short answer is, persistent overlay creates a persistent home directory that will remain in the environment even after reboot.
So what does that mean?
Well it simply means that as the live user you can download, save, create, and edit files in your home directory and they will be there the next time you start up the live Linux distribution. This means anything on your desktop or in your pictures, music, documents, or any other location in your home directory.
So what are the limitations of the overlay?
At this time the limitations of the persistent overlay is that they only encompass the home directory and no other, so if you install a program in any directory other than your home directory it will not be there again when you boot the Linux environment. Since the live USB stick is a quasi-live CD of sorts this limitation will more than likely be reoccurring until flash drives get to be large enough that an entire system could be stored on them.
So what makes this live CD to USB so different?
To be short, a USB stick has only so many reads and writes before it starts to wear out, to minimize the wear and tear on a flash drive you would want to minimize the amount of writes that there are to the flash memory. Too many writes to a flash drive can slow things down considerably and make the entire system appear like something is going wrong. To speed the system up it uses mostly RAM to read and write allowing for faster access to the files that would be possible using the slower flash memory.
What about a faster flash drive?
Well that would be all well and dandy but the simple fact is that there are no real standards for flash memory speed out in the market. Some claim that they are the fastest but benchmarks have proven most of them wrong. Optimizations in flash memory have created somewhat of a divide in the market, some are optimized for larger files and faster transfer speed while others are optimized for faster transfers with smaller files.
So how can I tell what type of flash drive I have?
Honestly, you can only tell by how quickly you can write small files to the flash drive. To test it download and install Firefox 3 portable, if it takes less than 90 seconds then you probably have a fast flash drive.
If it takes 2 minutes or more to install Firefox 3 portable then you most likely will have better transfers with larger files.
With all that in mind, as always if you have found this information useful leave a comment to let me know so.
Very usefull post.
Thanks.
P.S. I like your writing style.
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Unlike your other (spam?) commenters, this explanation isn’t detailed. a) How can I examine the contents of the persistent overlay on my SD/USB card (seems to be /LiveOS/overlay-MEDIANAME-XXXX-XXXX ) on another PC? b) If I install a new .iso, will Live USB Creator preserve my existing persistent overlay?
You are right about the comments, they are before I got akismet installed properly.
I am unaware of how to look at the contents of the persistent storage but I am sure that there is a way to mount the filesystem within a Linux system perhaps something like this will work,
mount -o ro /dev/live /mnt/liveWhere in theory you could use the name of the file instead of the /dev/live directory.
As far as I know when you create using the live-usb-creator it destroys the original overlay, but if you go the “old school” or “manual” way of creating the live usb you should be able to manually specify a persistent file.
Hope that helps.
Will the overlay work with other iso distributions such as CentOS 5.4 live CD?
I would think that this would work since Fedora and CentOS are based on RHEL, though your mileage may vary.