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I know for a fact, that Live CD versions of distros like Arch Linux, Debian, Fedora, Gentoo Linux, Salix, Ubuntu and on embedded distributions such as the OpenWrt and DD-WRT router firmware use SquashFS. But I was convinced, that optical media is practically bound to ISO9660 or UDF.

I was thinking, that it might be a good idea to use SquashFS for recovery partitions, as it works well on hard drives as well.

Another idea I had was: how about using it on other optical media? Most CD/DVD/BD-R is WORM anyway, so using SquashFS should be a step forward, given the transparent compression and all. I don't know if that would actually work though.

How do those non-UDF/ISO9660 filesystems on optical media work? Does it work anywhere else as well?

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Your question made me look around a bit, and this lwn.net thread might be interesting to you, too. (Doesn't seem to answer your question, though.) – sr_ Feb 4 '12 at 13:35
up vote 1 down vote accepted

You can put any filesystem on any block device you like. ISO9660 or UDF are generally used on optical media because that is what is usually expected. For instance, for the bios to boot from the cd, it must be in iso9660. Last time I tried, Windows ( XP ) wouldn't read UDF except on optical media, even though it seems to be a perfectly good fs to use on flash drives since it has the ability to store linux permissions but can also be recognized by windows ( just not on flash drives ). Rather silly of Microsoft to refuse to read it on flash drives if you ask me.

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Well, UDF has optimizations for hard drives as well. I haven't seem them being used on hard drives in the wild, though. – polemon Feb 6 '12 at 4:55
Since I'm just hanging around searching for an info about udf on flash drives, I have to correct you: udf does work in WinXP, but in read-only mode — it just needs some specific parameters, like specific blocksize (there're articles on this). In later WIndows versions it does work on read'n'write; so UDF is perfectly fine as a replacement for FAT. – Hi-Angel Feb 22 at 16:52
@Hi-Angel, got a pointer to these parameters? I'd love to see Windows actually mount a UDF flash drive. – psusi Feb 22 at 23:09
@psusi well, for example this one, or that one. – Hi-Angel Feb 22 at 23:11
@Hi-Angel, interesting.. I swear I tried exactly that setup before and found that XP would not mount it. That was about the time that I also patched linux to make better use of the no owner feature. I guess I'll have to try it again. – psusi Feb 22 at 23:56

I'd guess anything works as far as the operating system can understand it, after all it's a matter of reading bits and bytes and translating those to a filesystem structure.

About bootable optical devices, you just need to make sure that the El Torito part is there and that BIOSes can understand it, the rest is left to whatever OS is booted.

IIRC, Knoppix handles this by having a SquashFS image stored in a ISO9660 filesystem, probably to make sure it can be read by computers without SquashFS support (it has the cheat codes documentation there, along with some other useful stuff).

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