By default the version of mkinitrd provided in (or base on) Red Hat Enterprise Linux 5.3 attempts to include the dm-mem-cache module in the generated initial ramdisk images. Therefore when creating custom initial ramdisk images for kernels that do not provide the dm-mem-cache module, the mkinitrd command will fail with a message similar to:

No module dm-mem-cache found for kernel 2.6.18-92.1.13.el5, aborting.

To build an initrd image, for a kernel that does not provide the dm-mem-cache module, it is possible to prevent the inclusion of the module by adding the –without-dmraid argument to the mkinitrd command line.
It is also possible to create a permanent exception for the inclusion of the dm-mem-cache module. This can be done by creating the file /etc/sysconfig/mkinitrd/noraid as follows:

# echo “DMRAID=no” > /etc/sysconfig/mkinitrd/noraid
# chmod 755 /etc/sysconfig/mkinitrd/noraid