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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.

## Installation

Note:

- Reiser4 is still not included in the official Linux kernel, patches are provided to apply on the mainline 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).
- LILO is the only bootloader officially supporting Reiser4, but it seems to have issues when `/boot` is formatted as Reiser4
- Access Control Lists is not implemented and requires that journald either logs to a separate 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.

Install the reiser4progsAUR package which provides utilities for creating, fsck'ing and debugging Reiser4 volumes.

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

### Bootloader

Note:

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

It is recommended that you make a small (20-200mb) partition for `/boot` with a filesystem other than Reiser4, and then copy your `/boot` folder to the partition. Update your bootloader configuration accordingly, e.g. see #/boot/grub/grub.cfg.

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 encounter an error when trying to update `lilo.conf`. See #/etc/lilo.conf.

## 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

Below is the sample system this section will use as an example:

    # fdisk -l

    * /dev/sdxZ: (10 Gb, 5 Gb free); Reiserfs /mnt/oldroot
    * /dev/sdxY: (10 Gb, 10 Gb free); Reiser4 /
    * /dev/sdxW: (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:

- The defaults for mkfs.reiser4 includes enabled compression with the default algorithm being zstd.
  - To use either lzo or gzip instead of zstd, append `-o compress=lzo1` or `-o compress=gzip1`.
  - To disable compression altogether, use `-o create=reg40`.
- Additionally, the inline checksum plugin can be enabled with `-o node=node41`
- More information about the features, plugins and options is available in the documentation.

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

Since Reiser4 also has options specifically for SSD users as well, it is recommended to discard the partition upon creation of the filesystem, by adding the `-d` switch.

For drives with controllers already having hardware compression (like SandForce ones), it may be better to to disable the compression plugin, for example with an SSD:

    # mkfs.reiser4 -d -o create=reg40,node=node41 /dev/nvme0nXpY

### 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 a Live media and mount both your new Reiser4 partition and your current root partition. Then, just copy everything over like so:

    # cd /mnt
    # mkdir oldroot
    # mkdir reiser4
    # mount /dev/sdxZ 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/sdxY /mnt/reiser4
    # 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/sdxW bootpart
    # cp -R -a /mnt/oldroot/boot/* /mnt/bootpart/

Do not forget to edit your bootloader's configuration appropriately (see #Bootloader examples).

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

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/xY     /             reiser4 noatime,txmod=wa,onerror=remount-ro,discard 0   1
    /dev/xZ     /mnt/oldroot  ext4    defaults                                    0   0
    /dev/xW     /boot         ext2    defaults                                    0   1

## Bootloader examples

### /boot/grub/grub.cfg

    # (0) Arch Linux
    title  Arch Linux
    set root=(hdm,msdosn)
    kernel /vmlinuz-linux root=/dev/sdxY 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=(hdm,msdosn)
    kernel /vlinuz-linux root=/dev/sdaxY 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/sdx
    # 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/sdxY
            append="video=vesafb:1024x768-24@56,ywrap,mtrr splash=verbose,theme:darch console=tty1 resume2=swap:/dev/sdb1"
    initrd=/boot/initramfs-linux.img
    read-only

    image=/boot/vmlinuz-linux
            label=Arch
            root=/dev/sdxZ
            append="video=vesafb:1024x768-24@56,ywrap,mtrr splash=verbose,theme:darch console=tty1 resume2=swap:/dev/sdb1"
    initrd=/boot/initramfs-linux.img
    read-only

Then run:

    # lilo

## Troubleshooting

- Permissions: see chown.
- If you have problem with su after the change of filesystem, you should reinstall coreutils.

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- File systems