cloop sucks, squashfs rocks

[martinwguy]

Hi!
I just ran some tests on several compressed filesystems, and it turns
out that cloop has the worst performance in terms of caching of all of them.
Compressed filesystems gain space in a Live CD, but also speed because
less data has to read from the physical medium, and reading the CD itself
is usually the bottleneck.

Klaus once said:
zisofs is a compressed filesystem, cloop is a compressed
block device. Compressed filesystems are slower, because
each file has to be uncompressed again in each read, while
cloop keeps the uncompressed blocks in the normal block
layer filesystem cache. cloop is older, well-tested and
filesystem independent.

But, unlike all the other compressed read-only filesystems, cloop re-presents
a file that lives on the native CD filesystem as a new uncompressed filesystem,
and this means that the data are buffered twice: once in compressed form when
they are read from the native CD filesystem and once again after decompression.

To test this theory, I took a machine with 500MB RAM, got as much free RAM as
possible by running a 500MB process and killing it, got the tools (bash, tar, cat and
vmstat) into memory and then tarred up /opt from Knoppix 3.6 into /dev/null.
To read a total of 231380K it filled a total of 332548K of extra cache.

Now I don't know whether the cmpressed filesystems cache their data in
compressed or uncompressed form, but cloop caches it in both!
Apart from the fact that cloop does not give the best compression of the
full-feature compressed filesystems (squashfs was the best at that, sorry,
I don't have the figures to hand) cloop also beats the cache to death, and on a
memory-limited system, effective use of RAM and caching makes a big
difference to system performance.
And I would argue that for running a LiveCD most users are more
memory-limited than CPU-limited. 500MHz 128MB systems are common.

What about it, Klaus? ditch cloop? :)

M

[firnsy]

<rant></rant>

[martinwguy]

> I would say you have big balls throwing statements like that around without accurate figures at hand
1) Thankyou, I'll take that as a compliment!
2) What, six significant digits isn't accurate enough for you?

> Had cloop not been a project of Klaus
Ah! I didn't know that! Well, if it's his own, then it *must* be the best ;D
Sadly, egomania is the enemy of getting the best results.
That explains why everyone remasters knoppix with squashfs!

> if you're a squashfs fan
I'm not an anything fan. I'm a computer scientist and I evaluate the merits of
different solutions to the same problem by carefully measuring their performance.
Keep fanatism to football teams, where its partisan absurdity is obvious to everyone!
If, tomorrow, I find a better way of meanuring and it turns out that cloop or bumfs
gives better performance, I will recommend that.

Don't worry, cloop isn't the devil or poisonous or anything. It just doesn't get the
best compression and also incurs a big performance penalty on memory-limited
machines compared to the native compressed filesystems, which was the point
of my original post.

I think it's more useful to keep discussions at a technical level rather than
answering with personal insults. Thanks for the info on cloops "ownership"
though!

Bye
M

[firnsy]

I think it's more useful to keep discussions at a technical level rather than
answering with personal insults

I agree, and apologies for any offence cause ... The previous post has been sanitised.

Had I been a little more sober I would have gotten straight to the point which should have been, given your background, could you post a side by side comparison of say cloop vs squashfs (the best solution to day) to see the advantages and if any disadvantages.

[Jason W]

Me, I usually find memory to be the bottleneck. Granted, I run PC's that vary in ram from 64 to 128MB and with a processor of around 200 - 300 Mhz, and after searching high and low I have found Knoppix and its variants to be the fastest performing Linux livd CD's out there. And I am a Slackware fan and have been for 2 years. But I have been impressed with Debian/Knoppix performance here in the past month or so. I find Knoppix in the CD tray rivals Slackware on th HD in speed. Well, almost.
Slax uses the squashfs, and basic Slax even without any modules thrown in is less responsive than a full 700MB Knoppix CD even on my old hardware. I like Slax, but have to concede the better performance to Knoppix. Add modules to a Slax Live CD and you better have a new PC. But, sure, it is more to do with how Slax puts everything into memory more while Knoppix puts it there only when needed, than due to the compressed FS. I guess my point is why mess with a good thing.

[Fabianx]

>> Had cloop not been a project of Klaus
>Ah! I didn't know that! Well, if it's his own, then it *must* be the best ;D
>Sadly, egomania is the enemy of getting the best results.
>That explains why everyone remasters knoppix with squashfs!

If you think _that_ of Klaus you have catched the wrong person.

Klaus is just a very careful person, who you could also call conservative.

Remember also when Klaus used cloop there was _nothing_ else available and that squashfs
had some problems before. It might also be that UnionFS still has / had problems with squashfs.

I don't remember what was the case with zisofs though.

>Don't worry, cloop isn't the devil or poisonous or anything. It just doesn't get the
>best compression and also incurs a big performance penalty on memory-limited
>machines compared to the native compressed filesystems, which was the point
>of my original post.

Yes, you are right with those both, _BUT_ isofs is quite error-resistant and this get directly to cloop as there are just blocks that fail like on a normal CD.

I think it used to be an argument.also.

>I think it's more useful to keep discussions at a technical level rather than
>answering with personal insults.

Agree.

cu

Fabian