[Cerowrt-devel] Is there a particular reason cerowrt isn't using UBIFS?

Theodore Ts'o tytso at mit.edu
Sat Aug 30 21:38:37 EDT 2014

On Sat, Aug 30, 2014 at 02:57:05PM -0700, Dave Taht wrote:
> I tried ubifs in the early days. It doesn't squeeze stuff down even as good
> as jffs2, so the load of cerowrt exceeded 15mbyte. It does look to be an
> ever more reasonable answer once you have flash sizes greater than 128mbyte.

Another possible solution might be squashfs on top of ubi (instead of
mtdblock).  Ubi will provide the wear levelling and bad block
remapping, which mtdblock doesn't do.

> A thing that irks me in the age of 4G flash becoming fairly common is the
> general lack of compression aside from an option to btrfs. Debian barely
> fits into 2 gb

It depends on what you have installed, of course.  I have a debian
test image which gets used for ext4 testing which is 189 megabytes
uncompressed, and 57 megabytes using qcow2 compression (it gets run
using qemu/kvm)[1].  It's a basic debootstrap image plus a handful of
packages[2] plus xfstests (which is 22 megabytes uncompressed).

[1] ftp://ftp.kernel.org/pub/linux/kernel/people/tytso/kvm-xfstests/
[2] https://git.kernel.org/cgit/fs/ext2/xfstests-bld.git/tree/kvm-xfstests/test-appliance/packages

This is still much larger than 7 megabytes in the Cerowrt's root
image, granted, but it is possible to make a relatively svelte
debian-based image.

I've considered implementing MacOS X style compression (immutable
files, compression which happens in userspace, with decompression in
the kernel.)  The main reason why I haven't is that for most use
cases, space hasn't really been that much of an issue, or most of the
files are already compressed (i.e., Java or Dalvik classpath files
which are already zip compressed).  It wouldn't be _that_ hard to do,
but it's just not that high up on most people's priority lists.

    	      	       	       	  - Ted

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