GRAM is a kernel module based on the compression RAM Block Device ZRAM (https://www.kernel.org/doc/html/latest/admin-guide/blockdev/zram.html). The source code of ZRAM was reworked to remove compression, meaning it has the performance of ZRAM however but does not compress data. GRAM was created for DisTRaC https://github.com/DiamondLightSource/DisTRaC.

System Requirements:

• Linux Kernel 3.10.* (Tested on Redhat 7)
• Root privileges to create and remove block device

How to use

Creating the block device

To created the gram module run make inside the gram folder; this will produce the gram.ko file this is the kernel module.

To active, this kernel module run ./create.sh passing the number of RAM blocks (-n=) and size of the RAM block (-s=), running./create.sh -n=1 -s=50G will create 1 RAM Block with the size of 50G.

Running lsblk should return something similar, where the dots are other block devices details:

NAME               MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
.                   .   .    .    .    .  .       .
.                   .   .    .    .    .  .       .
gram0               252:0    0    50G  0 disk
.                   .   .    .    .    .  .       .

To create more block devices, increase the number speficifed in (-n=). ./create.sh -n=5 -s=10G will create 5 RAM blocks, each with a size of 10G.

Running lsblk should return something similar, where the dots are other block devices details:

NAME                MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
.                   .   .    .    .    .  .       .
.                   .   .    .    .    .  .       .
gram0               252:0    0    10G  0 disk
gram1               252:1    0    10G  0 disk
gram2               252:2    0    10G  0 disk
gram3               252:3    0    10G  0 disk
gram4               252:4    0    10G  0 disk
.                   .   .    .    .    .  .       .

These devices can be found in /dev/gram[0..N] where N is the number of devices.

To add physical and logical volumes to GRAM blocks, lvm.conf needs to be modified to accept GRAM types. Adding types = ['gram', 100] within devices{...} section will allow the creation of physical and logical volumes.

After creating physical and logical volumes, this device can be treated as a standard block device.

Removing the block device

To stop using GRAM remove any physical and logical volumes and run rmmod gram or run ./remove.sh this removes the block devices from the system, and free's the memory claimed.

To remove files created when running make run make clean bear in mind this will remove gram.ko.

Questions

If there are any questions, please contact scicomp@diamond.ac.uk