Ramdisk Size

Jeffrey B. Layton laytonjb at bellsouth.net
Mon Sep 22 14:34:04 EDT 2003


Tony Travis wrote:

> Eric R Johnson wrote:
>
>> I would like to create a large ramdisk to keep a database which will 
>> be searched often, but not changed.
>> The only thing I currently know how to do to create a ramdisk is:
>> mke2fs /dev/ram0
>> mount /dev/ram0 /tmp/ramdisk0
>>
>> The only problem is that this creates a 4MB ramdisk, and I would like 
>> something on the order of 1GB.
>
>
> Hello, Eric.
>
> Are you *sure* you want to do this?
>
> RAM disks are usually used for loading modules at boot time. That's 
> why they are small. Typically, the contents of a RAM disk are used as 
> a root filesystem for the kernel to load e.g. SCSI drivers, then 
> discarded when the 'real' root filesystem is mounted from SCSI disks. 
> People also use them to boot a 'minimal' Linux for diagnostics or for 
> some other reason. 


   Check out Warewulf: warewulf-cluster.org. Very cool cluster
distribution that uses a very small Ramdisk to hold the necessary
parts of the OS. I've just started to use it and it's very slick.

(snip)

> However, I think it would be better to use 'tmpfs' for a 1Gb RAM 
> filesystem. The kernel will provide fast access to the most frequently 
> accessed areas of your database held in RAM, but it will move the less 
> frequently accessed areas onto the swap device freeing up RAM for your 
> programs and for other disk caches. 


   What's the difference between tmpfs and a ramdisk created through
the kernel? Is there a speed difference?

BTW, here's a link on creating a generic ram disk:

http://www.lissot.net/partition/ramdisk.html

(read the bottom part).

   If you are happy with the speed improvement of using a ram disk
to store the database, you might want to consider squashfs
(http://squashfs.sourceforge.net/) It's a read-only filesystem that you
can use to reduce the size of the required ram disk. You will take a
hit in speed, but perhaps the ram disk will make up for it. Oh, and
you will have to patch the kernel to use it.

Good Luck!

Jeff


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