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Background

Persistent live systems with Ubuntu store the data to persist in a file named 'casper-rw' or partition labeled 'casper-rw'. In addition there can be a file or partition 'home-rw' to store the data of the home directory.

Other linux distros use 'live-rw', 'persistence' or other naming conventions.

Questions

  • What format is better for casper-rw file ext2, ext3 or ext4, why?

  • What format is better for casper-rw partition ext2, ext3 or ext4, and why?

  • Parameters would be performance, size, limitations, etc.

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    For what purpose ? Your question is very broad. See anything from en.wikipedia.org/wiki/Comparison_of_file_systems to linux-magazine.com/Online/Features/Filesystems-Benchmarked to phoronix.com/… – Panther Sep 14 '17 at 2:27
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    for use in live iso persistence... – ZEE Sep 14 '17 at 2:35
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    Persistent live systems and the file systems used in the file or partition, where the data are stored to persist is a rather limited and specific subject. I do not agree that it is too broad, and suggest to reopen the question. – sudodus Sep 14 '17 at 10:41
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    The question is very broad and is asking about performance, size, and limitations of various file systems. Even if it were narrowed, which file system should I use for persistence it is still quite broad. Do you have benchmarks on file systems specific to persistence ? And of course I suppose as always it depends on what you are doing. – Panther Sep 14 '17 at 13:16
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    The main problem you will have with persistence is that is it a cow system. The limitations of persistence have very little to do with what filesystem you use. Persistence will work fine for minor changes for example saving themes or customization to your interface across boots, saving wireless networks and passwords, install a few packages, etc. – Panther Sep 14 '17 at 13:21
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File system for the casper-rw file or partition

The ext4 file system is more advanced than the previous ext2 and ext3 file systems. It is the standard file system used in many linux distros, and is well debugged and polished.

ext4 and ext3 have journaling, which helps a lot, when there are problems with the file system, and the file system must be repaired. But journaling causes additional write operations to the drive, and if it is USB pendrive or memory card, it can cause excessive wear of the memory cells. You can turn off journaling.

  • ext2 works well without tweaks in a USB pendrive or memory card, but I would recommend ext4 with journaling turned off.

  • In an SSD or HDD I suggest that you use ext4 with journaling turned on (which is the default).

    Please notice that the casper-rw partition need not be in the same drive as the persistent live operating system. This works with all Ubuntu versions, when booting via grub, and I have read (but not tested yet) that the newest version of syslinux can manage it too.

  • I suggest the same choice of file system for casper-rw files and partitions.

File system for the home-rw file or partition

If you create a home-rw file or partition, the standard advice is to use the same file system and tweaks as for the casper-rw partition. But there is an alternative, that makes it available to Windows.

I am experimenting with the UDF file system for home-rw. It works well with Ubuntu persistent live systems, and when the [USB pen]drive is plugged into a computer running Windows, it will be mounted with read/write permissions, so that files can be transferred easily between the Ubuntu persistent live system and Windows.

Installed system in an external drive

If you want an up to date system with full flexibility concerning what to install, you should use an installed system, installed into an external drive like it were installed into an internal drive. Such a system can be portable between computers too, but not as portable as a persistent live system.

Links

Some claim on the internet that persistence reduces lifespan of the USB stick. Is this true?

help.ubuntu.com/community/Installation/UEFI-and-BIOS#Final_system_tweaks

help.ubuntu.com/community/mkusb/persistent#Partitions

Experimenting with the UDF file system for home-rw

Boot Ubuntu from external drive

  • I think your answer proves the question is not too broad, well done. When you get a chance could you please update your answer with a comment on using the UDF file system for home-rw. A lot of people might like to be able to open home folder in Windows. – C.S.Cameron Aug 7 '18 at 18:23
  • I am experimenting with the UDF file system for home-rw. It works well with Ubuntu persistent live systems, and when the [USB pen]drive is plugged into a computer running Windows, it will be mounted with read/write permissions, so that files can be transferred easily between the Ubuntu persistent live system and Windows. – sudodus Aug 7 '18 at 18:37
  • I have tried your udf2home-rw script, People coming to this thread because they want info on custom USB installations might find it interesting. I can understand that writing to a closed post is not much fun, but it is getting some votes for reopen. – C.S.Cameron Aug 7 '18 at 20:43

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