Reiser4

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Reiser4 is the successor filesystem for ReiserFS, initially designed and developed entirely from scratch by Namesys and Hans Reiser. It is very efficient in handling many files (often used in /var for this purpose) and includes a plugin-based design with plugins with features such as intelligent transparent compression, both inline data and meta-data checksums through the crc32c algorithm with added optional mirrors and failover support through its own implementation of subvolumes.

More information about the features, plugins, design and mkfs or mount options is described in detail here.

Important Notes

Reiser4 requires a patched kernel.
It consumes a little more CPU than other filesystems (just like Btrfs). To avoid having issues on laptops using TLP for power saving, it is recommended to disable the options for SATA Link power saving in /etc/default/tlp (again, as with Btrfs).
Even LILO as the only bootloader officially supporting Reiser4 seems to have issues with it when /boot is formatted as Reiser4
It is still not included in the official Linux kernel, but patches for Linux-5.x is already available.
Access Control Lists is not implemented and as of linux-5.x.x requires that Systemd/Journal either logs to a seperate logging daemon or to Tmpfs. Another workaround is to compile systemD by source without ACL support, but is not recommended.

Tip: Gparted LiveCD is a small Linux distribution booting straight into Gparted. It also supports Reiser4 and can be used to migrate from an existing filesystem to Reiser4

Packages

1. Install the reiser4progs^AUR package which provides utilities for creating, fsck'ing and debugging Reiser4 volumes.

2. You will need a Reiser4 patched kernel. Patches can be found here or at the more recently created Git repository which is maintained by its current lead developer, the mathematician and programmer Edward Shishkin.

3. Bootloader (Optional, only needed if you want to format your / (root, including /boot) as Reiser4)

Note: Backing up your bootloader configuration file should be considered if one is going to have /boot residing on a Reiser4 volume.

a) Recommended: make a small (as mentioned above, 20-200mb) partition for /boot with a filesystem other than Reiser4 with GParted, and then copy your /boot folder to the partition. Update your bootloader configuration accordingly, eg. with Grub2 do:

# grub-mkconfig -o /boot/grub/grub.cfg.

Note: EFI systems in general require a FAT32 partition for booting the kernel and thus it may be advantageous or unproblematic to have the /boot directory residing on that partition instead of only the EFI directory. Many EFI-users have their whole /boot directory on their ESP

b) If you do not use EFI and wish to put everything including /boot on a Reiser4 partition (not recommended) you will need to use LILO. This is not advised, as you will probably get an error when trying to update lilo.conf:

# lilo

4. Reboot

Note: The following steps are for using Reiser4 as your / (root, including /boot). If you just want to use Reiser4 as root with /boot mounted on the ESP you should modify the following instructions according to your needs.

Moving to Reiser4

In the next steps we will copy the data from your current root partition to the new Reiser4 partitions. Make sure you have enough disk space on the Reiser4 partition with:

# df -h

Sample system

# fdisk -l
* /dev/sda1: (10 Gb, 5 Gb free); Reiserfs /mnt/reiser4
* /dev/sda2: (10 Gb, 10 Gb free); Reiser4 /
* /dev/sda3: (200 Mb, 180 Mb free); ext2 /boot

Formatting

Since Reiser4 supports different transaction models optimized for different types of storage media (SSDs, HDDs), the options used while formatting and mounting will differ.

Note: For users with traditional HDDs, the defaults listed below will be enough.

Keep in mind that the defaults for mkfs.reiser4 includes enabled compression with the default algorithm being Zstd.

If one wishes to use either lzo or gzip instead of Zstd, it is needed to append

-o compress=lzo1

or

-o compress=gzip1

If one wishes to disable compression altogether, one must append:

-o create=reg40

to the

mkfs.reiser4

command. Additionally, the inline checksum plugin can be enabled with

-o node=node41

More information about the features, plugins and options is available here.

Note: With X being your partition number!

mkfs.reiser4 /dev/sdaX
mkdir /mnt/reiser4
mount -t reiser4 -o txmod=journal,noatime,onerror=remount-ro /dev/sdaX /mnt/reiser4

It is recommended and also the default to use the Cryptcompress plugin by formatting with the following options:

mkfs.reiser4 -o create=ccreg40 /dev/sdaX

Since Reiser4 also has options specifically for SSD users as well, it is recommended to discard the partition upon creation of the filesystem, the -d switch can be applied as shown below:

mkfs.reiser4 -d -o create=ccreg40,compress=Zstd1 /dev/nvme0n1X

For drives with controllers already having hardware compression (like SandForce ones), it may be better to to disable the compression plugin.

For HDDs:

mkfs.reiser4 -o create=reg40,node=node41 /dev/sdX

For SSDs:

mkfs.reiser4 -d -o create=reg40,node=node41 /dev/nvme0n1pX

Copy system

Once the partition is formatted, copy you current system to the new partition and create the system directories. You may either do this from Arch Linux, or to make it easier (so that you do not have to use makedev later), just boot up with the Gparted LiveCD and mount both your new Reiser4 partition and your current root partition. Then, just copy everything over (as root) like so:

cd /mnt
mkdir oldroot
mkdir reiser4
mount /dev/sdaX oldroot

Depending on what transaction model one wish to use which are optimized for different types of storage media, the mount option txmod=wa (for SSDs), txmod=journal (for HDDs) must be defined when mounting the partitions through the -o switch. The default is txmod=hybrid which heuristically alternates between the "wa" (write-anywhere) and "journal" models for optimized performance on rotating disks while trying to avoid excess fragmentation at the same time.

mount -t reiser4 -o txmod=hybrid,noatime,onerror=remount-ro /dev/sdaY reiser4 (the Reiser4 partition)
cp -R -a /mnt/oldroot/* /mnt/reiser4/

Then, you need to mount your /boot partition, and if you have not already, copy /boot from your original root partition over to it.

Note: It is suggested to empty your /boot from the Reiser4 partition to use it as a mountpoint, which is reflected later in your fstab

mkdir bootpart
mount /dev/sdaZ bootpart
cp -R -a /mnt/oldroot/boot/* /mnt/bootpart/

Do not forget to edit your bootloader's configuration appropriately (see examples at the bottom of the article).

Note: In case you upgraded grub before rebooting you may need to manually install grub to your /boot partition, otherwise, things may break and prevent you from booting. In this case using a LiveCD to Chroot and would be your last hope.

/etc/fstab:

Note: If you can confirm that Reiser4 works for you, you should format the old root partition.

#
# /etc/fstab: static file system information
#
# <file system>	<dir>	      <type>  <options>	         <dump>	<pass>

/dev/nvme0n1p1  /             reiser4 noatime,txmod=wa,onerror=remount-ro,discard 0   1
/dev/sda2       /mnt/oldroot  ext4    defaults                                    0   0
/dev/sda3       /boot         ext2    defaults                                    0   1

Bootloader Examples

/boot/grub/grub.cfg:

# (0) Arch Linux
title  Arch Linux
set root=(hd0,msdos3)
kernel /vmlinuz-linux root=/dev/sda3 ro rootfstype=reiser4 rootflags=noatime,txmod=journal,onerror=remount-ro init=/usr/bin/bootchartd
initrd /initramfs-linux.img

# (1) Arch Linux
title  Arch Linux Fallback
set root=(hd0,msdos3)
kernel /vlinuz-linux root=/dev/sda3 ro rootfstype=reiser4 rootflags=noatime,txmod=journal,onerror=remount-ro
initrd /initramfs-linux-fallback.img

Then run:

# grub-mkconfig -o /boot/grub/grub.cfg

/etc/lilo.conf:

#
# /etc/lilo.conf
#

boot=/dev/hda
# This line often fixes L40 errors on bootup
# disk=/dev/hda bios=0x80

default=Arch4
timeout=20
lba32
prompt
compact

image=/boot/vmlinuz-linux
        label=Arch4
        root=/dev/hda5
        append="video=vesafb:1024x768-24@56,ywrap,mtrr splash=verbose,theme:darch console=tty1 resume2=swap:/dev/hdb1"
initrd=/boot/initramfs-linux.img
read-only

image=/boot/vmlinuz-linux
        label=Arch
        root=/dev/hda3
        append="video=vesafb:1024x768-24@56,ywrap,mtrr splash=verbose,theme:darch console=tty1 resume2=swap:/dev/hdb1"
initrd=/boot/initramfs-linux.img
read-only

Then run:

# lilo

Troubleshooting

Permissions: chown -R username.group <userdir>
If you have problem with su command after the change of fs, you should reinstall coreutils package.