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Old 03-02-2009, 01:21 PM   #1
kushalkoolwal
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Difference between these two kernel options?


Hi,

I have been wondering for quite some time as to what is the difference between the following two kernel options:
Code:
RAM block device support (BLK_DEV_RAM)

Saying Y here will allow you to use a portion of your RAM memory as
a block device, so that you can make file systems on it, read and
write to it and do all the other things that you can do with normal
block devices (such as hard drives). It is usually used to load and
store a copy of a minimal root file system off of a floppy into RAM
during the initial install of Linux.

Note that the kernel command line option "ramdisk=XX" is now obsolete.
For details, read <file:Documentation/blockdev/ramdisk.txt>.

To compile this driver as a module, choose M here: the
module will be called rd.

Most normal users won't need the RAM disk functionality, and can
thus say N here.
and

Code:
Initial RAM filesystem and RAM disk (initramfs/initrd) support (BLK_DEV_INITRD)

The initial RAM filesystem is a ramfs which is loaded by the
boot loader (loadlin or lilo) and that is mounted as root
before the normal boot procedure. It is typically used to
load modules needed to mount the "real" root file system,
etc. See <file:Documentation/initrd.txt> for details.

If RAM disk support (BLK_DEV_RAM) is also included, this
also enables initial RAM disk (initrd) support and adds
15 Kbytes (more on some other architectures) to the kernel size.

If unsure say Y.
I understand that the BLK_DEV_INITRD option is necessary for booting using initrd image (as Debian does by default). Then in what scenario will BLK_DEV_RAM be used?
 
Old 03-02-2009, 01:35 PM   #2
mesiol
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Hi,

first option is for RAM disk running a filesystem for example for speeding up temporary files (we used this on a virus scanner machine to speed up scanning and prevent from large disk IO).

The second option is for initial RAM disk used at system startup for decompressed initrd image as temporary root file system.
 
Old 03-02-2009, 01:40 PM   #3
kushalkoolwal
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Quote:
Originally Posted by mesiol View Post
Hi,

first option is for RAM disk running a filesystem for example for speeding up temporary files (we used this on a virus scanner machine to speed up scanning and prevent from large disk IO).
Interesting...Do you know good pointers which explains in detail how we can setup up a system which just boots on RAM?
 
  


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