RAMDisk Blues

RAMDisk Blues

[Ivan Passos]

Hello,

I'm trying to boot a Linux system that has the following configuration:
- 32MB of Flash (IDE Flash Drive), where a kernel image and a compressed
  root filesystem image are stored.
- 256MB of RAM, 128MB of which will be used as a RAMDisk (believe me, this
  is cheaper than 128MB Flash + 128MB RAM ... :).

After looking for information on how to do that on the 'Net and in the
Documentation/ directory of the kernel src, I've been able make the Flash
Drive bootable. Unfortunately, it's bootable, but it doesn't boot
successfully ... :(

What I tried:
- Compressed the image I used to boot the system from a regular IDE HD to
  a file called rd_image.gz (~20MB compressed), and copied it to the IDE
  Flash Drive.
- Compiled a 2.4.6 kernel with RAMDisk and initrd support built-in, and
  then copied it to the IDE Flash Drive.
- Ran LILO with the following config. file (based on the doc. I found so
  far):

	boot=/dev/hda		# The FlashDrive device
	install=/boot/boot.b
	map=/boot/map
	append="ramdisk_size=131072 initrd=rd_image.gz"
	vga=normal
	default=Linux
	delay=5
	image=/boot/vmlinuz
		initrd=/boot/rd_image.gz
		root=/dev/ram0
		label=Linux
		read-only

LILO completes the operation without problems (no errors). However, when I
boot the system from the FlashDrive, this is the output I get:

LILO Loading Linux ......................................................
..............................................

That's it!! The system hangs at this point (it really hangs, to the point
that the "soft" power on/off doesn't work anymore, and I have to turn off
the system from the back in order to reboot it).

What am I doing wrong?? Is my RAMDisk image too big (I thought there was
no limit, as long as you had enough RAM ...)?? Does anyone here know a
good resource on the 'Net where I can find more detailed information about
creating a RAMDisk-based Linux system that boots from a device other than
a floppy disk?? Most of the docs I found were related to boot / rescue /
utility floppies, so I don't know whether this is the right way to do it
or not ...

Any help would be appreciated.

Later,
Ivan

Re: RAMDisk Blues

[Nick DeClario]

Hi,  I know there is this option in the kernel:

Default RAM disk size
CONFIG_BLK_DEV_RAM_SIZE
  The default value is 4096. Only change this if you know what are
  you doing. If you are using IBM S/390, then set this to 8192.

I grabbed that from ~/linux/Documentation/Configure.help.  I have never
gone about changing this before as the largest RAM disks I have delt
with were no larger than 3Mb.  But it defaults to 4Mb, so perhaps
increasing this would solve your problem.

	-Nick

Ivan Passos wrote:
> 
> Hello,
> 
> I'm trying to boot a Linux system that has the following configuration:
> - 32MB of Flash (IDE Flash Drive), where a kernel image and a compressed
>   root filesystem image are stored.
> - 256MB of RAM, 128MB of which will be used as a RAMDisk (believe me, this
>   is cheaper than 128MB Flash + 128MB RAM ... :).
> 
> After looking for information on how to do that on the 'Net and in the
> Documentation/ directory of the kernel src, I've been able make the Flash
> Drive bootable. Unfortunately, it's bootable, but it doesn't boot
> successfully ... :(
> 
> What I tried:
> - Compressed the image I used to boot the system from a regular IDE HD to
>   a file called rd_image.gz (~20MB compressed), and copied it to the IDE
>   Flash Drive.
> - Compiled a 2.4.6 kernel with RAMDisk and initrd support built-in, and
>   then copied it to the IDE Flash Drive.
> - Ran LILO with the following config. file (based on the doc. I found so
>   far):
> 
>         boot=/dev/hda           # The FlashDrive device
>         install=/boot/boot.b
>         map=/boot/map
>         append="ramdisk_size=131072 initrd=rd_image.gz"
>         vga=normal
>         default=Linux
>         delay=5
>         image=/boot/vmlinuz
>                 initrd=/boot/rd_image.gz
>                 root=/dev/ram0
>                 label=Linux
>                 read-only
> 
> LILO completes the operation without problems (no errors). However, when I
> boot the system from the FlashDrive, this is the output I get:
> 
> LILO Loading Linux ......................................................
> ..............................................
> 
> That's it!! The system hangs at this point (it really hangs, to the point
> that the "soft" power on/off doesn't work anymore, and I have to turn off
> the system from the back in order to reboot it).
> 
> What am I doing wrong?? Is my RAMDisk image too big (I thought there was
> no limit, as long as you had enough RAM ...)?? Does anyone here know a
> good resource on the 'Net where I can find more detailed information about
> creating a RAMDisk-based Linux system that boots from a device other than
> a floppy disk?? Most of the docs I found were related to boot / rescue /
> utility floppies, so I don't know whether this is the right way to do it
> or not ...
> 
> Any help would be appreciated.
> 
> Later,
> Ivan
> 
> -
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-- 
Nicholas DeClario
Systems Engineer                            Guardian Digital, Inc.
(201) 934-9230                Pioneering.  Open Source.  Security.
nick@guardiandigital.com            http://www.guardiandigital.com

Re: RAMDisk Blues

[Ivan Passos]

On Tue, 17 Jul 2001, Nick DeClario wrote:

> Hi,  I know there is this option in the kernel:
>
> Default RAM disk size
> CONFIG_BLK_DEV_RAM_SIZE
>   The default value is 4096. Only change this if you know what are
>   you doing. If you are using IBM S/390, then set this to 8192.
>
> I grabbed that from ~/linux/Documentation/Configure.help.  I have never
> gone about changing this before as the largest RAM disks I have delt
> with were no larger than 3Mb.  But it defaults to 4Mb, so perhaps
> increasing this would solve your problem.

This is set to 131072 (128MB). Just to make sure, I also set it on the
lilo.conf in the append line, with "ramdisk_size=131072". Maybe there is a
limitation in the RAMDisk driver and it doesn't work well with huge
RAMDisk sizes??

Any other hints?!?!

Later,
Ivan