Hello,

I need to know the minimum partition size one can create using Ext4 and minimum partition size one can create using Btrfs.

Consider the minimum block size in Ext4 is 1024 Bytes and Btrfs is 4096 Bytes.

Regards,
Deb

Why ?

Homework, perhaps?

Deb;

It is usually a good idea to tell us why you want to answer a question like this---look at you last question back in Feb.

As for the specific question---why not try it?

I want to know this, as in many websites I found only Max. filesystem size, but not minimum size. I have to choose between Ext4 and Btrfs for some system, and this is one of the parameters.
I also created filesystem of various sizes, but couldn't come to any conclusion.
Hope I have answered your question "why"

Not really because the minimum sizes are smaller than to be of practicable use.

So--take EXT4 for example. If the minimum block size is 1024 bytes---I assume that means the space available to store data. There is then some overhead required---if the EXT4 spec. does not describe this, then you have a minimum of 2 options:
1. Dig thru a working partition and see how much space is being used for overhead.
2. Try smaller and smaller sizes until you find the limit. This will be tedious---at least using fdisk, I can't create a new partition and install a file system without rebooting
Let's take a wild guess that EXT4 requires 20 blocks of overhead---add one block for data, and you have a minimum partition size of 21 blocks, but you can only store 1Kbyte. Is this useful? Probably not-----but tell us exactly what the system is supposed to be doing, and maybe there will be a better answer.

*shrug* you don't need us to test that: just 'dd bs=1 count=1024' (or less) some /dev/random to a file, loop-mount it, create your file system, check and if it is accessible create smaller ones.

By invoking "mkfs.btrfs" I get message that 256MB is required at least. For ext4 you can use "resize2fs -P /dev/sd??" to get approximated minimum size (it depends on journal, inode size, etc., with 1MB nad 1kB blocks it prints 2353 blocks in my system).

It would be quick to create a virtual filesystem in a file, e.g.
The limit of an ext4 filesystem should be 4096 blocks of 512 bytes, that is about 2 Mb. It depends on the minimum size to store the filesystem journal, other than inode and superblock sizes that are smaller. This is from a theoretical point of view, since - as already pointed out - a physically minimum filesystem is not usable.

Edit: beaten by unSpawn!

It would make sense that mkfs.btrfs demanded a minimum size other than a theoretical minimum.

It is a modern file system that doesn't have to conform to any legacy rules. Ext4 has legacy issues.

Shrinking volumes could render tools useless too.

The idea of using such a modern file system with advanced features and making it as small as possible is a contradiction.

So, nothing to do with partitions per se at all ...

Maybe a partition issue. I didn't ponder on that at all.

Red Hat docs say that / needs to be 250M but that doesn't mean that you can't create a partition with less space. Indeed I have has some old systems that only had a 4M hard drive and multiple partitions.

Maybe if you don't trust encrypted flash drives and you don't want to monthly force yourself to remember a 20 digis /#*numbers_capital_etters_small_letters_numbers password, you can think to a micro encrypted volume for a backup on unsafe google or ms drive...