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Old 05-23-2012, 03:36 AM   #1
paldebojyoti
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Minimum Partition Size


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
 
Old 05-23-2012, 05:28 AM   #2
jv2112
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Why ?
 
Old 05-23-2012, 06:14 AM   #3
pixellany
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Quote:
Originally Posted by jv2112 View Post
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?
 
Old 05-24-2012, 04:30 AM   #4
paldebojyoti
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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"
 
Old 05-24-2012, 04:33 AM   #5
catkin
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Quote:
Originally Posted by paldebojyoti View Post
Hope I have answered your question "why"
Not really because the minimum sizes are smaller than to be of practicable use.
 
Old 05-24-2012, 05:47 AM   #6
pixellany
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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
Quote:
I have to choose between Ext4 and Btrfs for some system, and this is one of the parameters.
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.
 
Old 05-24-2012, 05:58 AM   #7
unSpawn
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Quote:
Originally Posted by paldebojyoti View Post
I need to know the minimum partition size one can create using Ext4 and minimum partition size one can create using Btrfs.
*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.
 
Old 05-24-2012, 06:05 AM   #8
eSelix
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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).
 
Old 05-24-2012, 06:12 AM   #9
colucix
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Quote:
Originally Posted by pixellany View Post
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
It would be quick to create a virtual filesystem in a file, e.g.
Code:
 $ dd if=/dev/zero of=disk-image count=4096
4096+0 records in
4096+0 records out
2097152 bytes (2.1 MB) copied, 0.0406892 s, 51.5 MB/s
$ ls -l disk-image
-rw-r--r--. 1 colucix users 2097152 May 24 12:04 disk-image
$ /sbin/mkfs -t ext4 -q disk-image
disk-image is not a block special device.
Proceed anyway? (y,n) y
$ file disk-image 
disk-image: Linux rev 1.0 ext4 filesystem data (extents) (huge files)
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!

Last edited by colucix; 05-24-2012 at 06:16 AM.
 
Old 05-25-2012, 09:24 PM   #10
jefro
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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.

Last edited by jefro; 05-25-2012 at 09:27 PM.
 
Old 05-26-2012, 02:18 AM   #11
syg00
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So, nothing to do with partitions per se at all ...
 
Old 05-26-2012, 11:43 AM   #12
jefro
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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.

Last edited by jefro; 05-26-2012 at 11:48 AM.
 
  


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