Re: ANNOUNCEMENT: Squashfs released (a highly compressed filesystem)

Jeff Garzik
2002-10-30T03:57:28Z

Phillip Lougher wrote:

> Samuel Flory wrote:
>
>> Phillip Lougher wrote:
>>
>>> Hi,
>>>
>>> First release of squashfs. Squashfs is a highly compressed
>>> read-only filesystem for Linux (kernel 2.4.x). It uses zlib
>>> compression to compress both files, inodes and directories. Inodes
>>> in the system are very small and all blocks are packed to minimise
>>> data overhead. Block sizes greater than 4K are supported up to a
>>> maximum of 32K.
>>>
>>> Squashfs is intended for general read-only filesystem use, for
>>> archival use, and in embedded systems where low overhead is needed.
>>>
>>> Squashfs is available from http://squashfs.sourceforge.net.
>>>
>>> The patch file is currently against 2.4.19. There is further info
>>> on the filesystem design etc. in the README.
>>>
>>> I'l be interested in getting any feedback, advice etc. on it.
>>>
>>
>> What are the advantages of squashfs vs cramfs?
>>
>>
>>
>
> Cramfs was the inspiration for squashfs. Squashfs basically gives
> better compression, bigger files/filesystem support, and more inode
> information.
>
> 1. Blocks upto 32K are supported - data is compressed in units of 32K
> which achieves better compression ratios than compressing in 4K
> blocks. Generally using bigger than 4K blocks are a bad idea, because
> the VFS calls the filesystem in 4K pages. Squashfs explictly pushes
> the extra block data into the page cache.

I'm curious if you looked at ntfs-tng's code before implementing this.
It's pretty darned optimal...

> 2. Squashfs compresses inode and directory information in addition to
> file data. Inodes/directories generally compress down to 50%, or say
> on average 8 bytes or less per inode.

squashfs or mksquashfs?

A r/w compressed filesystem would be darned useful too :)

Jeff