Awesome

Zramdrive

Usefull for IoT / maker projects for reducing SD, Nand and Emmc block wear via write operations. Uses Zram to minimise precious memory footprint and extremely infrequent write outs.

Uses an OverlayFS lower bind mount of /var/log to /opt/zram and upper zram to create fast startups and extremely small memory requirements. On stop uses https://github.com/kmxz/overlayfs-tools merge tool to merge from volatile ram to persistant. Many thanks kmxz for providing one of the only overlayfs tools available.

Works well in conjunction with https://github.com/StuartIanNaylor/log2zram and https://github.com/StuartIanNaylor/zram-swap-config Can not be used for mission critical applications where a system crash and data loss is unaceptable. If the extremely unlikely event of a system crash is not a major concern then Zramdrive can massively reduce block wear whilst maintaining and extremely tiny memory footprint whilst increasing i/o perf. Further resilience can be added by the use of a watchdog routine to force stop or full blown battery backup.

Works well in conjunction with https://github.com/StuartIanNaylor/zram-swap-config and https://github.com/StuartIanNaylor/log2zram

Install

sudo apt-get install git
git clone https://github.com/StuartIanNaylor/zramdrive
cd zramdrive
sudo sh install.sh

Customize

variables :

In the file /etc/zramdrive.conf sudo nano /etc/zramdrive.conf to edit:

# Size for the zram memory used, it defines the mem_limit for the zram device.
# The default is 20M and is basically enough for minimal applications.
# Because aplications can vary in space requirements this may have to be tweaked to suit application .
SIZE=20M
# COMP_ALG this is any compression algorithm listed in /proc/crypto
# lz4 is fastest with lightest load but deflate (zlib) and Zstandard (zstd) give far better compression ratios
# lzo is very close to lz4 and may with some binaries have better optimisation
# COMP_ALG=lz4 for speed or deflate for compression, lzo or zlib if optimisation or availabilty is a problem
COMP_ALG=lz4
# DISK_SIZE is the uncompressed disk size. Note zram uses about 0.1% of the size of the disk when not in use
# DISK_SIZE is expected compression ratio of alg chosen multiplied by SIZE where 300% is an approx good level.
# lzo/lz4=2.1:1 compression ratio zlib=2.7:1 zstandard=2.9:1
# Really a guestimate of a bit bigger than compression ratio whilst minimising 0.1% mem usage of disk size
DISK_SIZE=60M
# HDD_DIR is the persistant directory that your bind will move the old directory to.
# Can be any name often and /var or /opt are valid locations but can be placed anywhere
HDD_DIR=/opt/moved
# ZRAM_DIR is the directory that will firstly moved to HDD_DIR then mounted as Zram with data copied
# ZRAM_DIR is the live zram drive of the directory you wish to use
ZRAM_DIR=/var/cache
# Zram & mount directories default can be changed if wished
ZDIR=/opt/zram

It is working?

pi@raspberrypi:~ $ df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/root        15G  1.2G   13G   9% /
devtmpfs        460M     0  460M   0% /dev
tmpfs           464M     0  464M   0% /dev/shm
tmpfs           464M  6.2M  458M   2% /run
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           464M     0  464M   0% /sys/fs/cgroup
/dev/mmcblk0p1   44M   22M   22M  50% /boot
/dev/zram0      1.5G  8.5M  1.4G   1% /opt/zram/zram0
overlay0        1.5G  8.5M  1.4G   1% /var/log
/dev/zram1       55M   84K   50M   1% /opt/zram/zram1
overlay1         55M   84K   50M   1% /var/cache
tmpfs            93M     0   93M   0% /run/user/1000

…
pi@raspberrypi:~ $ zramctl
NAME       ALGORITHM DISKSIZE  DATA COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram0 lz4           1.5G   37M  1.5M  1.9M       4 /opt/zram/zram0
/dev/zram1 lz4            60M  4.2M  4.9K   68K       4 /opt/zram/zram1

/dev/zram1 zramdrive working with zram0 log2zram

Compressor name	Ratio	Compression	Decompress.
zstd 1.3.4 -1	2.877	470 MB/s	1380 MB/s
zlib 1.2.11 -1	2.743	110 MB/s	400 MB/s
brotli 1.0.2 -0	2.701	410 MB/s	430 MB/s
quicklz 1.5.0 -1	2.238	550 MB/s	710 MB/s
lzo1x 2.09 -1	2.108	650 MB/s	830 MB/s
lz4 1.8.1	2.101	750 MB/s	3700 MB/s
snappy 1.1.4	2.091	530 MB/s	1800 MB/s
lzf 3.6 -1	2.077	400 MB/s	860 MB/s

Uninstall

sudo sh /usr/local/bin/zramdrive/uninstall.sh

$HDD_DIR is retained on uninstall and only removed on new install.

Git Branches & Update

From the command line, enter cd <path_to_local_repo> so that you can enter commands for your repository. Enter git add --all at the command line to add the files or changes to the repository Enter git commit -m '<commit_message>' at the command line to commit new files/changes to the local repository. For the <commit_message> , you can enter anything that describes the changes you are committing. Enter git push at the command line to copy your files from your local repository to remote.