On Sat, 30 Aug 2014, Theodore Ts'o wrote:
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.
One other place this sort of thing is likely to be useful is for Raspberry Pi
and other small (embedded by some defintions) systems that use SD cards for
their OS system. The I/O to the storage is so slow that the saved I/O time is
likely to more than cover the cost of the decompression.
Raspberry Pi systems have had to move to 4G cards as their base because it's
just not possible to have the standard install do more than boot on a 2G card.
David Lang
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