How can I change the amount and size of Linux ramdisks (/dev/ram0

How can I change the amount and size of Linux ramdisks (/dev/ram0 - /dev/ram15)?

Using Linux, when I boot I automatically have 16 16MB ramdisks, however, I would like to create one really large ramdisk to test some software.

I found that I can adjust the size of the ramdisks already on the system with the kernel boot parameter ramdisk_size however, this makes all 16 ramdisks (/dev/ram0 - /dev/ram15) the size that is specified. So if I want to create a 1GB ramdisk, I would need 16GB of memory.

Basically, I want to create one 10GB ramdisk which would be /dev/ram0. How would I go about doing that? I assume there is a kernel boot parameter, but I just haven't found it.

Answer

There are two kernel configuration options that you can set in your .config file:

CONFIG_BLK_DEV_RAM_COUNT=1
CONFIG_BLK_DEV_RAM_SIZE=10485760

This configured my kernel to create one ramdisk that is 10G at boot time.

Notes:

CONFIG_BLK_DEV_RAM_SIZE is in KB.

Don't specify more memory than you actually have RAM in your computer.

In menuconfig look under Device Drivers->Block Devices.

You can specify the size of the ram disks you create via the kernel boot parameter ramdisk_size. For example:

kernel /vmlinuz-2.6.32.24 ro root=LABEL=/ rhgb quiet ramdisk_size=10485760

Now I can boot my machine and make a file system on it, mount it and use it exactly like a block device.

# mkfs.xfs /dev/ram0
# mount /dev/ram0 /mnt/ramdisk

Sources:

http://www.vanemery.com/Linux/Ramdisk/ramdisk.html [dead]

https://www.kernel.org/doc/Documentation/blockdev/ramdisk.txt

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