Re: PXES Using compressed root filesystem (cramfs)

[email protected] wrote:

>Hi,
>
>I first must say I have been extremely impressed with how flexible & powerful 
>PXES has become. Especially been able to easily tweak the configuration using
>the Remote Configuration option without having to rebuild the image. 
>
>I was just wondering if anyone has previously looked at using a transparent
>compression filesystem for the initrd (root filesystem?) or if there any plans
>in the future for PXE to uses a compressed filesystem.
>
Next release of PXES will include squashfs, I'm testing it. With this 
filesystem type you will need ~12Mb for the root filesystem and ramdisk 
(same size).

>
>I just thought I might share my experience with getting PXES to work with a
>compressed root filesystem.
>
>I had a couple of workstations that had only 32Mb of RAM that I wanted to get
>working under PXES. However the most basic configuration of PXES with the
>RDesktop client with XFree 4.3.0 weigh in at around 22Mb or (8-9Mb gzipped)
>[3.3.6 very limited support for video cards]. Unfortunately the image was too
>large and the kernel constantly paniced when attempting to run it under 32Mb. 
>
>I tried manually pulling out drivers from the initrd image (mounting the initrd
>image and rm file I didn't think I needed) which helped but didn't help enough.
>I worked out that there was only at most 9-10Mb free to run X and the kernel
>after the 22Mb ramdisk for the root image.
>
>What got me thinking was that the difference between the compressed initrd
>(root filesystem) image and the uncompressed initrd (root filesystem) was 13Mb. 
>The ramdisk was obviously using most of the memory available and any savings
>there would definately make a huge difference.
>
>>From past experience I knew there was some worked done on compressed
>filesystems in linux. I did some searching and located a couple of options.
>cramfs (Supported by the 2.4 kernel natively [Read Only])
>jffs2 (Not yet native in the liunx kernel [Read/Write] Design for Flash memory)
>
>As cramfs (although read-only) was already supported in the 2.4 kernel I
>thought that would be the best to try. I compiled a new kernel 2.4.23 with the
>config options for 2.4.20 supplied with PXES + cramfs. 
>
>Mounted the uncompressed loopback initrd image with and ran 
>mkcramfs /mnt/loop /tftpboot/pxes/pxes-0.7-cramfs.initrd
>I ran into problems with the mkcramfs supplied with Redhat 7.3. It wouldn't
>properly mount the root filesystem. I was able to locate a new version of
>cramfsprogs 1.1 which worked better from sourceforge.
>
>http://sourceforge.net/projects/cramfs/
>
>cramfsprog brought down the initrd image size to around 10Mb. 
>Which is an instant 12Mb saving as the cramfs initrd image doesn't need
>expanding.
>
>I had to add another parameter to the pxes\pxelinux.cfg\default (Boot file).
>ramdisk_blocksize=4096 
>
>This tells the kernel that the root filesystem is using 4096 (cramfs default) as
>the block size instead of the normal 1024 (ext2 default for small filesystems).
>
>So the default (Boot file) read something like
>label 1
> kernel vmlinuz-2.4.23-cramfs.i586
> append ramdisk_size=10000 ramdisk_blocksize=4096 ro
>initrd=pxes-0.7-cramfs.initrd root=/dev/ram
>
>The above append line on one line.
>
>Booted up a workstation and it worked. I was able to boot XFree 4.3.0 and
>rdesktop in 32Mb of RAM. Using the cramfs would had added some overhead but I
>was unable to see a significant slowdown (Although I wasn't looking too hard)
>
>Using cramfs allowed me to run PXES on a 32Mb workstation as now I had 18 -
>20Mb of memory available to run the kernel and XFree 4.3.0.
>
>The biggest downside of using cramfs is that when you build the cramfs image it
>is *mostly* a one way process. It is not that simple to make modifications to
>the cramfs initrd image (Although I did read that there is a uncramfs util). 
>
Thank you very much for the info.
I hope next release solve your problems.

>
>Daryl,
> 
>
>
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