UnionFS

[lilsirecho]

Typical description of the UnionFS is that the ramdisk is "stacked on top of" the r/o CD/DVD in Knoppix3.8 Cebit for example.

The limitations of the Unionfs with respect to RAM availability are not discussed in typical descriptions of the system.

Are there any users who can provide some light on the limitations within unionfs?

[rcook]

A good description of the UNion FS. It talks about copy up, where if you open a file on the ro file systemas rw, the file is copied up to the rw file system. I suspect this would be your greatest problem in terms of RAM usage i.e. if you open a large file in the ro system to write, it will hit your RAM disk. If you are adding new files, etc you will only hit the RAM for the directory and the file.

[lilsirecho]

rcook;
Pleased to have a response to my querry.

In my computer I have 3GB of ram and don't expect to have a problem in respect to ram use.

The understanding of limits in use of the Unionfs is important for all users which is why I posed the question of limits.

It is well to be informed of limits!!

[lilsirecho]

Googling reveals that the persistent home directory can be utilized to retain the UnionFS elements downloaded and retained in ramdisc.

I assume the contents of ram disk Unionfs elements are uncompressed since the apt-get install function was utilized. The result is a large impact on the persistent home size(assumption).

Since the mechanism exists to retain the downloaded applications, it would seem possible to transfer the persistent home record of the applications, reboot to the HDD and copy the contents of persistent home to a working directory.

This working directory could then be utilized for other purposes. Perhaps this directory lacks essentials provided by the CD?

It would seem that the capacity of the ramdisc might limit the size of downloaded Unionfs applications. If the system has 3GB of ram, does this level of ram permit the download of ~2GB (some overhead and 700MB of CD) of apps?

If the user has 1GB of Unionfs apps in ramdisc, can the ramdisc content be compressed (previously assumed to be uncompressed) and thereby reduce the persistent home size?

If the user chooses TORAM mode what impact has this mode on the performance of the UNionfs parameters?

[carfield]

Isn't there a tool for me to persist content in RAMDISK to HDD/USB disk? Otherwise it not really useful... I have to make sure that there is enough RAM and my machine never shutdown...

[LadyPixel]

Ok... maybe I just don't want my hopes crushed but... tell me, in unambiguous terms:

Is it really impossible for me to burn knoppix on a DVD, install new software, and somehow save the changes to that DVD so that the next time i boot up, the changes are still there?

Can you partition a DVD? (clutching for straws now )

If i have a 256MB flash drive, can i save the changes there so that when i reboot unionfs will do its magic or is it just home directories that are saved? ( really clutching cuz i can't afford one now)

Ummm.... is there another Live CD that can let me do the first thing, or is it still impossible?

Thanx.

[lilsirecho]

Further notes on the UNIONFS as observed here.

I find that with the Cebit 3.8 KNOPPIX that after booting it to desktop and using commandline ..su, followed by df -h, the listing of file systems includes UNIONFS. The listing reports the size of UNIONFS is 9.1GB total and 5.5GB is used.

Examination of the properties of UNIONFS reveals 1.4GB file size.

Examination of the size of KNOPPIX shows 1.6GB.

These reports were given from a CD booted version of Cebit 3.8 KNOPPIX.

It would seem that the data derived from ..df -h... is erroneous when determining UNIONFS file size or does not apply to that FS.

Furthermore, when the same procedure is applied to the new 3.8.1 KNOPPIX, the UNIONFS size is limited to 4.5GB.

It would seem that the either the procedure is limited to compressed file systems or that the UNIONFS is mis-reported in the ....df -h....command.

I assume(I hope correctly) that those programs installed through the UNIONFS apt-get install are installed in uncompressed format as opposed to the original programs which appear in compressed format. This would seem obvious since the re-mastering procedures require such downloaded programs to be mkisofs compressed in order to load them to a re-mastered CD.

Note to LadyPixel;

I have spent some weeks with a procedure outlined in the DVD forum which permits a "split" .iso to be generated.

This procedure separates the "boot" process in a "prefix.iso" from the KNOPPIX/KNOPPIX "suffix.iso" and ties the two together in a concatenation step to produce a final .iso for DVD+RW burn.

I have used the procedure to burn a 748MB burn to DVD+RW on the Cebit 3.8Version which added ~50MB of new programs to the burn. It performs well.

The limit of DVD capacity for compressed format data is 4.4GB. It takes perhaps 3000 apps to obtain that level of installed programs.

Use of DVD+RW allows for many experimental trials in working with the "split" .iso method.

I observe that the UNIONFS contains some indications that a similar "mapper" technique is utilized, altho, in my observation, does not utilize the apps in compressed format.

The procedure used in the "split.iso" technique requires the generation of KNOPPIX/KNOPPIX added applications in the same compressed-fs used in version 3.8 KNOPPIX using mkisofs procedures to generate the new /KNOPPIX compressed file. This file then replaces the original file in the 3.8 KNOPPIX version.

This produces a "suffix.iso" which is concatenated with the "prefix.iso" previously generated per the outlined procedure for the "split.iso".

The procedure did produce a re-master with greater than 700MB of data (more than a CD size) and burned to a DVD+RW.

I have yet to establish a DVD with 3GB or more of compressed apps.

If one saves the elements making up the "split" changes could be added at will with a new Burn to the DVD+RW.

The method described calls for a lot of HDD capacity for a full-sized DVD.

One comment: UNIONFS seems not to be well-described...its new....


Edit: I have successfully burned a DVD+RW with 3.8GB of data utilizing Video files installed in the "prefix.iso" rather than the "suffix".iso. This was a test of the "split" system to verify that it can exceed 2GB file size on a DVD burn.

This system enables the full data recording capability for DVD+RW media and, if compressed files are provided in the "suffix.iso" of the "split" system, 9GB of apps are possible(many thousands of applications!).

[ICPUG]

LadyPixel,

There is a version of Puppy Linux (Multi-session CD) that will save changes back to CD.

I have not tried it. This version is still an alpha release.

Puppy is a compact distro so it does not contain the same/as many apps as Knoppix. Nevertheless it is quite interesting, especially if you are used to Windows 9x as the desktop looks remarkably familiar!

ICPUG