User:Ali3nx/Installing Gentoo Linux EFISTUB On ZFS

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Install Gentoo Linux on OpenZFS using EFIStub Boot

Author: Michael Crawford (ali3nx)


This guide will show you how to install Gentoo Linux on AMD64 with:

 * UEFI-GPT (EFI System Partition) - This will be on a FAT32 unencrypted partition as per UEFI Spec.
 * /, /home/username, on segregated ZFS datasets
 * /home, /usr, /var, /var/lib zfs dataset containers created for pool dataset structure
 * swap on regular partition
 * OpenZFS 0.8.6
 * efistub boot without Grub
 * genkernel initramfs
 * systemd or openrc
 * Gentoo Stable (amd64)

Why efistub boot!? grub works for everyone!

  • UEFI bios motherboards have been the default on all modern computer hardware since around 2013 entirely depreciating legacy bios.
  • The modernization and wide availability of UEFI motherboards has retired the mandatory requirement for software bootloaders such as grub.
  • grub itself when UEFI booted uses efistub to boot both itself and linux OS installs. This additional interference is unnecessary to boot Linux.
  • Intel has publicly stated that legacy bios CSM compatibility switch support will be entirely depreciated on new hardware manufactured after 2020 forcing use of true uefi boot modes

Why not use grub with zfs!?

  • The wiki guides for zfsroot from zfsonlinux and many distros all advise using grub bootloader which can work however grub doesn't fully support the newest zfs pool feature flags and using grub can be an added risk as well as added complication that can be entirely mitigated by using a uefi boot efistub configuration to boot your zfs root pool directly.
  • The risk of using grub with zfs arises from the lack of modern pool feature support for zfsonlinux which requires the administrator tread carefully to ensure that a global zpool upgrade is never run or your zfsroot configuration becomes unbootable due to the legacy zfs pool feature flags required for grub to function having been upgraded. Such an occurrence having happened cannot be undone and recovery would require some major surgery from a livecd.
  • Building a new system install initially using a legacy configuration implies additional ongoing maintenance be accepted to maintain a legacy configuration.
  • zfs rootfs dataset encryption is easier to configure utilizing efistub boot.

Required Tools

Download the System Rescue CD + ZFS ISO

You will need to download Fearedbliss modified System Rescue CD that includes ZFS from one of the mirrors on his profile page.

LiveUSB Creation

We will be creating a UEFI Bootable USB since this guide will be showing you how to install Gentoo Linux on ZFS with UEFI Enabled.

For the following commands, we will assume that your USB is /dev/sdg.

Format the USB
root #parted -a optimal /dev/sdg
(parted)mklabel msdos
(parted)mkpart primary 1 -1
(parted)set 1 boot on
Disk /dev/sdg: 8192MiB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags: 

Number  Start    End      Size     Type     File system  Flags
 1      1.00MiB  8191MiB  8190MiB  primary               boot, lba
Create the FAT32 Filesystem on the USB

We will now create the FAT32 filesystem on the USB. This needs to be FAT32 since this is the filesystem used in the UEFI Specification. The label we will use for this partition will be in the following format SYSRCDXYZ, where XYZ is the version number of the System Rescue CD you downloaded.

For example, if you are using System Rescue CD 6.1.3, the label will be SYSRCD613.

root #mkfs.fat -F32 -n SYSRCD613 /dev/sdg1
Make folders to mount USB and ISO
root #mkdir /tmp/usb
root #mkdir /tmp/sysresccd
Mount your USB and your ISO
root #mount -o loop,ro sysresccd-6.1.3_zfs_0.8.4.iso /tmp/sysresccd
root #mount /dev/sdg1 /tmp/usb
Copy files over from ISO to USB
root #rsync -avP /tmp/sysresccd/ /tmp/usb/

And that's it! You now have a Bootable UEFI USB.


Rufus is the USB Utility I recommend when on Windows for Feardbliss zfs iso. You can Download Rufus here.

  1. Start Rufus
  2. Select your USB Device from the Device drop down.
  3. Select GPT partition label type and UEFI Non-CSM options
  4. Do not use MBR or uefi boot will not function
  5. Select Fat 32 Filesystem
  6. Select your ISO by clicking SELECT.
  7. Click START.

This should be all that's necessary to have a Bootable UEFI USB.


  • Only installing Gentoo on one drive called /dev/sda (or /dev/nvme0n1, etc)
  • Fearedbliss System Rescue CD + ZFS iso is being used.
  • genkernel is being used as your initramfs.
  • gentoo-sources is being used as your kernel.

Boot your system into the zfs LiveUSB

Since this is highly computer dependent, you will need to figure out how to boot your USB on your system and get to the live environment. You may need to disable Secure Boot if that causes your USB to be rejected. Make sure your system BIOS/UEFI is set up to boot UEFI devices, rather than BIOS devices (Legacy).

Confirm that you booted in UEFI Mode

After you booted into the Live CD, make sure that you booted into UEFI mode by typing the following:

root #ls /sys/firmware/efi

If the above directory is empty or doesn't exist, you are not in UEFI mode. Reboot and boot into UEFI mode.

Continuing the installation without being in UEFI mode will most likely yield an unbootable system. If you want to install in BIOS mode, you will need a different setup.


We will now partition the drive and aim to create the following layout:

/dev/sda1   | 512 MB        |   EFI System Partition                | /efi
/dev/sda2   | 32768 MB      |   swap                                | swap
/dev/sda3   | Rest of Disk  |   ZFS                                 | /, /home/username ...
There are many UEFI motherboard firmwares that are extremely buggy. We will attempt to use a 512 MiB FAT32 partition configuration to increase success.
512MB esp will be beneficial to provide adequate space the 250MB genkernel initramfs file.

Open up your drive in GNU parted and tell it to use optimal alignment:

root #parted -a optimal /dev/sda
Keep in mind that all of the following operations will affect the disk immediately. GNU parted does not stage changes like fdisk or gdisk.

Create GPT partition layout

This will delete all partitions and create a new GPT table.

Larger swap will accommodate hibernation should that be desired. 32GB swap is used in the below example to accommodate many different hardware configurations.

(parted)mklabel gpt

Create and label your partitions

(parted)mkpart esp fat32 1 513
(parted)mkpart swap linux-swap 513 33280
(parted)mkpart rootfs ext4 33280 100%

parted does not offer a zfs filesystem type so ext4 is used temporarily. the filesystem label name is largely autodetected and as a result will become irrelevant after zpool creation.

Set the bootable flag on the ESP partition

(parted)set 1 boot on

Final View

Model: Virtio Block Device (virtblk)
Disk /dev/vda: 500GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system     Name    Flags
 1      1049kB  513MB   512MB   fat32           esp     boot, esp
 2      513MB   33.3GB  32.8GB  linux-swap(v1)  swap
 3      33.3GB  500GB   467GB                   rootfs

Exit the application


Format your drives

Format your uefi esp partition

root #mkfs.vfat -F32 /dev/sda1
This partition needs to be FAT32 due to it being an UEFI requirement. If it isn't, your system will not boot!

Create your swap

root #mkswap -f /dev/sda2
root #swapon /dev/sda2
  • Do not put your swap inside a zvol. System lockups are possible when RAM is 100% and the system starts swapping while the swap is on ZFS. There has been an open unresolved bug in Openzfs regarding this is and as a result is best avoided. Swap memory pressure doesn't crash when the swap is on a normal partition.

Determine disk/by-id identifier

Using traditional block device identifiers such as /dev/sda or /dev/nvme0n1 with zfs can work but can also be undesirable due to the possibility of a block device name changing. Something as simple as connecting a usb storage device can cause this to occur.

Should this ever happen zfs pools are unaware of the change having occurred which can render a zfs pool inoperable. Use of non generic device specific disk identifiers which are also identified by disk serial number is more desirable for use with zfs as a result of this complication. This also provides added utility advantages for identifying a faulty disk in larger zfs pools.

To determine the non generic ata disk identifier id type the following

root #ls -l /dev/disk/by-id

lrwxrwxrwx 1 root root 9 Mar 2 11:28 ata-Samsung_SSD_860_EVO_500GB_serialnum -> ../../sda
lrwxrwxrwx 1 root root 10 Mar 2 11:28 ata-Samsung_SSD_860_EVO_500GB_serialnum-part1 -> ../../sda1
lrwxrwxrwx 1 root root 10 Mar 2 11:28 ata-Samsung_SSD_860_EVO_500GB_serialnum-part2 -> ../../sda2
lrwxrwxrwx 1 root root 10 Mar 2 11:28 ata-Samsung_SSD_860_EVO_500GB_serialnum-part3 -> ../../sda3

Nvme storage devices would resemble this example

root #ls -l /dev/disk/by-id

lrwxrwxrwx 1 root root 13 Mar 2 11:28 nvme-Samsung_SSD_960_PRO_512GB_serialnum -> ../../nvme0n1
lrwxrwxrwx 1 root root 15 Mar 2 11:28 nvme-Samsung_SSD_960_PRO_512GB_serialnum-part1 -> ../../nvme0n1p1
lrwxrwxrwx 1 root root 15 Mar 2 11:28 nvme-Samsung_SSD_960_PRO_512GB_serialnum-part2 -> ../../nvme0n1p2
lrwxrwxrwx 1 root root 15 Mar 2 11:28 nvme-Samsung_SSD_960_PRO_512GB_serialnum-part3 -> ../../nvme0n1p3

Generally using /dev/disk/by-id/ata-disk or /dev/disk/by-id/nvme-disk is more desirable to ensure the disk block device is more specific.
There may be /dev/disk/by-id/wmm or /dev/disk/by-id/nvme-eui.
Use of these block device identifiers in the example below should be avoided if possible for use with this guide.

root #ls -l /dev/disk/by-id/wwn*

lrwxrwxrwx 1 root root 10 Mar 2 11:28 wwn-0x5002538e40aba28d-part1 -> ../../sda1
lrwxrwxrwx 1 root root 10 Mar 2 11:28 wwn-0x5002538e40aba28d-part2 -> ../../sda2

root #ls -l /dev/disk/by-id/nvme*

lrwxrwxrwx 1 root root 13 Mar 2 11:28 nvme-eui.0025385971b064dd -> ../../nvme0n1
lrwxrwxrwx 1 root root 15 Mar 2 11:28 nvme-eui.0025385971b064dd-part1 -> ../../nvme0n1p1

Create your zpool

Create your zpool which will contain your drives and datasets:

xattrs and posixacl are enabled to provide support for modern filesystem security features. Relative atime updates which are a global default in ext4 are enabled as well.

xattrs is necessary for proper functionality of systemd-journald

Substitute ata-disk1-part3 for nvme-disk1-part3 if you have an nvme ssd disk.

root #zpool create -f -o ashift=12 -o cachefile=/etc/zfs/zpool.cache -O compression=lz4 -O xattr=sa -O relatime=on -O acltype=posixacl -O dedup=off -m none -R /mnt/gentoo rpool /dev/disk/by-id/ata-disk1-part3

Create your rootfs zfs datasets

Create the dataset container structure and dataset necessary for /.

root #zfs create -o mountpoint=none -o canmount=off rpool/ROOT
root #zfs create -o mountpoint=/ rpool/ROOT/gentoo

Set the boot flag for zfs root dataset

root #zpool set bootfs=rpool/ROOT/gentoo rpool

Create /usr, /var, /var/lib and /home zfs dataset containers

Creation of several unmounted dataset containers is necessary to provide dataset structure for the zfs pool. Creation of these containers after install is complete can be disruptive, involved and best completed before filesystem contents are written to disk to ensure the system will boot.
Dataset containers for /usr and /var especially benefit from this having been completed in advance.
This structures datasets within the pool for correct dataset segregation.
The /var/lib dataset container is created to allow for easy creation of /var/lib/foo datasets for system or network services if desired at a later date.

rpool/home dataset container is created to segregate user home directory dataset contents from the rootfs dataset for improved rootfs dataset incremental snapshot size management to ensure that rootfs snapshots do not fill the available pool storage space.

Additional accomodation must be made when using systemd with zfs to ensure that zfs /home dataset container is not configured to use a mountpoint as systemd may attempt to create a new /home directory on system boot causing the user home directory datasets to fail to mount on system boot due to a pool import mountpoint conflict.

Creating the rpool/home dataset container using the canmount=off option omitting a directory mountpoint ensures this complication will be unlikely to occur.

root #zfs create -o canmount=off rpool/usr
root #zfs create -o canmount=off rpool/var
root #zfs create -o canmount=off rpool/var/lib
root #zfs create -o canmount=off rpool/home

Create user home directory dataset

Replace username with the desired user name

root #zfs create -o mountpoint=/home/username rpool/home/username

Verify everything looks good

You can verify that all of these things worked by running the following:

root #zpool status
  pool: rpool
 state: ONLINE
  scan: none requested

        NAME        STATE     READ WRITE CKSUM
        rpool       ONLINE       0     0     0
          vda3      ONLINE       0     0     0

errors: No known data errors
I created a qemu vm to provide the zpool status representation. qemu and the livecd I used did not provide /dev/disk/by-id for qemu virtual disks. If installing on bare metal hardware this should not be a complication.
root #zfs list
rpool                1.20M   418G       96K  none
rpool/ROOT            192K   418G       96K  none
rpool/ROOT/gentoo      96K   418G       96K  /mnt/gentoo
rpool/home            192K   418G       96K  none
rpool/home/username    96K   418G       96K  /mnt/gentoo/home/username
rpool/usr              96K   418G       96K  none
rpool/var             192K   418G       96K  none
rpool/var/lib          96K   418G       96K  none

Now we are ready to install Gentoo!

Installing Gentoo

Set your date and time

We use ntpdate to set accurate time,date and hardware clock to mitigate clock skew that can cause software compilation to malfunction

root #ntpdate -u

2 Mar 19:32:19 ntpdate[12777]: adjust time server offset 0.454897 sec

Preparing to chroot

First let's mount our efi boot partition in our chroot directory:

root #cd /mnt/gentoo
root #mkdir efi
root #mount /dev/sda1 efi

We'll use the Oregon State University Gentoo Linux mirror.
If you desire use a different regional mirror from the official Gentoo Linux mirror list

Download the systemd amd64 stage3 system archive and extract it

root #wget <file>
root #tar xJpvf stage3-*.tar.xz --xattrs-include='*.*' --numeric-owner

Copy zpool cache

root #mkdir etc/zfs
root #cp /etc/zfs/zpool.cache etc/zfs

Copy network settings

root #cp --dereference /etc/resolv.conf /mnt/gentoo/etc/

Mounting the necessary filesystems

root #mount --types proc /proc /mnt/gentoo/proc
root #mount --rbind /sys /mnt/gentoo/sys
root #mount --make-rslave /mnt/gentoo/sys
root #mount --rbind /dev /mnt/gentoo/dev
root #mount --make-rslave /mnt/gentoo/dev

Entering the new environment

root #chroot /mnt/gentoo /bin/bash
root #source /etc/profile
root #export PS1="(chroot) ${PS1}"

Inside the chroot

Edit fstab

Use of disk UUID's to denote block devices entries in fstab has become the more desirable default to ensure an unpredicted block device alteration never renders a filesystem unmountable as a result of fstab becoming inaccurate.
Something as simple as connecting a usb storage device to a booted system has been known to cause this to occur.
The blkid command reveals these disk identifiers that are available for disk partitions created on gpt disk partition labels.
Despite having created disk partition names disk UUID's are more specific.

root #blkid

/dev/loop0: TYPE="squashfs"
/dev/vda1: UUID="9E40-2218" TYPE="vfat" PARTLABEL="esp" PARTUUID="ce3ca4f8-bf90-42ae-9ed3-fbd34a718fd9"
/dev/vda2: UUID="fac87c68-50ef-424b-9673-dfd0a9890aff" TYPE="swap" PARTLABEL="swap" PARTUUID="5475ac59-f72a-40eb-80f1-7a634bc04f5c"
/dev/vda3: LABEL="rpool" UUID="3195477004188779862" UUID_SUB="13330732843625778565" TYPE="zfs_member" PARTLABEL="rootfs" PARTUUID="7997947d-1530-4c4e-be93-c76b6c966822"
/dev/sr0: UUID="2019-09-27-14-03-43-10" LABEL="Gentoo amd64 latest" TYPE="iso9660" PTUUID="2db7a891" PTTYPE="dos"

Everything is on zfs so we don't need anything in here except for the boot and swap entries. fstab should resemble the following example. Substitute the provided UUID's from your blkid command:

root #nano /etc/fstab

UUID=9E40-2218                              /efi            vfat            noauto,defaults    1 2
UUID=fac87c68-50ef-424b-9673-dfd0a9890aff   none            swap            sw                 0 0

Modify make.conf

Let's modify our /etc/portage/make.conf so we can start installing stuff with a good base (Change it to what you need):

root #nano /etc/portage/make.conf

USE="caps cgroup-hybrid"

# This should be your number of processors + 1

EMERGE_DEFAULT_OPTS="--with-bdeps y --complete-graph y"

# knight rider rides again!
FEATURES="candy fixlafiles unmerge-orphans"

Get the portage tree

Copy the default example portage config

root #mkdir /etc/portage/repos.conf
root #cp /usr/share/portage/config/repos.conf /etc/portage/repos.conf/gentoo.conf
root #emerge-webrsync

Install required applications

Now install the initial apps:

root #emerge dracut bash-completion eix gentoolkit genkernel efibootmgr dosfstools gentoo-sources linux-firmware cronie intel-microcode parted

Kernel Configuration

Reviewing the current gentoo-sources Linux kernel version

Gentoo provides eselect to manage many core system environment variables including the active /usr/src/linux symlink.

root #eselect kernel list

Available kernel symlink targets:

 [1]   linux-5.4.92-gentoo *

The command result of eselect should match the active linux kernel symlink

root #ls -l /usr/src/

total 9
lrwxrwxrwx 1 root root 20 Mar 3 00:20 linux -> linux-5.4.92-gentoo
drwxr-xr-x 26 root root 39 Mar 3 00:20 linux-5.4.92-gentoo

Necessary kernel configuration features

efistub boot relies on a key Linux kernel configuration feature to function

KERNEL Linux kernel 3.3+
---> Processor type and features
         [*] EFI runtime service support

sys-fs/zfs requires Zlib kernel support (module or builtin).

General Architecture Dependent Options --->
  GCC plug ins  --->  
    [ ]   Randomize layout of sensitive kernel structures 
Cryptographic API --->
  <*> Deflate compression algorithm
Security options  ---> 
  [ ] Harden common str/mem functions against buffer overflows

sys-apps/systemd relies on the following menu options provided by sys-kernel/gentoo-sources

Gentoo Linux --->
  [*] Gentoo Linux support
  [*]   Linux dynamic and persistent device naming (userspace devfs) support
  [*]   Select options required by Portage features
        Support for init systems, system and service managers  --->
          [*] systemd
          [*] openrc

Invoke the Linux kernel configuration menu

The Linux kernel provides a console based configuration menu. Select the required configuration features in addition to necessary configuration features for your hardware.

root #cd /usr/src/linux
root #make menuconfig

Compile the Linux kernel

root #cd /usr/src/linux
root #make && make modules_install install

Install zfs software and kernel module

sys-fs/zfs and sys-fs/zfs-kmod must be installed after kernel configuration is complete

Install ZFS software

root #emerge sys-fs/zfs-kmod sys-fs/zfs

Enable zfs systemd services- Systemd Only

root #systemctl enable
root #systemctl enable zfs-import-cache
root #systemctl enable zfs-mount
root #systemctl enable

Enable zfs openrc services - Openrc Only

root #rc-update add zfs-import boot
root #rc-update add zfs-mount boot
root #rc-update add zfs-share default
root #rc-update add zfs-zed default

Generate and verify the zfs hostid file

This is necessary for genkernel initramfs generation and zfs pool import integrity verification

root #zgenhostid
root #file /etc/hostid

Installing the gentoo-sources kernel binary

Install the kernel

root #mkdir -p /efi/efi/gentoo
root #cd /efi/efi/gentoo
root #cp /boot/vmlinuz-5.4.92-gentoo vmlinuz-5.4.92-gentoo.efi

Generate and copy initramfs file to its correct location

Genkernel initramfs works good for most configurations and provides an alternative initramfs creation and management option where dracut may be experiencing difficulties importing zfs pools at system boot. I've experienced this with some configurations using fast ssd storage pools. When this abundance of performance was available dracut loaded the initramfs too fast causing a latency delay loading the zfs kernel module consequentially causing pool import failure on system boot. Reproducing this behavior can be hit or miss if kernel module modprobe latency ever does occur during initramfs processing.

To attempt to introduce additional processing latency into a genkernel initramfs to slow down initramfs processing a solution was devised to include the entire linux-firmware contents into a genkernel initramfs. This worked very well for many months however this purposefully bloated initramfs when uncompressed is very large and may not function with some common home pc motherboards. My server as can be seen below is an older model supermicro enterprise server motherboard and has no disagreements with being force fed a 600MB uncompressed initramfs image at system boot.

If your able to use dracut and dracut works do use dracut. If you prefer to use genkernel you can at your desire to not include the --firmware option to create a sensibly sized genkernel initramfs.

Recently my server has been using a dracut initramfs with dual vdev ssd mirror pool and experienced no pool import failure concerns but when those do occur using a different initramfs has resolved those complications.

Using a dracut initramfs

root #dracut --hostonly -k /lib/modules/5.4.92-gentoo/ --kver 5.4.92-gentoo -f /boot/initramfs-5.4.92-gentoo.img
root #cd /efi/efi/gentoo
root #cp /boot/initramfs-5.4.92-gentoo.img .

Using genkernel initramfs

root #genkernel initramfs --zfs --firmware --compress-initramfs --microcode-initramfs --kernel-config=/usr/src/linux/.config
root #cd /efi/efi/gentoo
root #cp /boot/initramfs-5.4.92-gentoo.img .

Installing the bootloader onto your drive

We will need to configure the bootloader entry in uefi firmware to direct boot the linux kernel and initramfs.

The following command will install the uefi bootloader entry in uefi firmware referencing the kernel and initramfs located at /efi/efi/gentoo

Edit the Linux kernel version to the desired current version used.

root #efibootmgr --disk /dev/sda --part 1 --create --label "Gentoo ZFS 5.4.92" --loader "efi\gentoo\vmlinuz-5.4.92-gentoo.efi" --unicode 'root=ZFS=rpool/ROOT/gentoo ro initrd=\efi\gentoo\initramfs-5.4.92-gentoo.img'

efibootmgr will print the uefi firmware loader table contents upon success also revealing the updated boot order

root #efibootmgr

BootCurrent: 0001
Timeout: 0 seconds
BootOrder: 0003,0001,0000,0002
Boot0000* UiApp
Boot0001* UEFI QEMU DVD-ROM QM00001
Boot0002* EFI Internal Shell
Boot0003* Gentoo ZFS 5.4.92

Final steps before reboot

root #passwd
root #exit
root #reboot

After you reboot

Take a snapshot of your new system

Since we now have a working system, we will snapshot it in case we ever want to go back or recover files:

root #zfs snapshot rpool/ROOT/gentoo@2020-03-02-0000-01-INSTALL
root #zfs snapshot rpool/home/username@2020-03-02-0000-01-INSTALL

You can view the status of these snapshots using the zfs command

root #zfs list -t snapshot

ZFS dataset snapshot automation

sys-fs/zfs-auto-snapshot can be installed and configured to provide dataset snapshot automation.

root #emerge sys-process/cronie sys-fs/zfs-auto-snapshot

Enable the system service and start cronie cron daemon as required for functionality of zfs-auto-snapshot.

root #systemctl enable cronie.service
root #systemctl start cronie.service

Configure daily and weekly snapshot generation for rpool/ROOT/gentoo

root #zfs set com.sun:auto-snapshot:daily=true rpool/ROOT/gentoo
root #zfs set com.sun:auto-snapshot:weekly=true rpool/ROOT/gentoo

Limiting the ARC size

If you want to cap the ZFS ARC from growing past a certain point, you can put the number of bytes inside the /etc/modprobe.d/zfs.conf file, and then remake your initramfs. When the system starts up, and the module is loaded, these options will be passed to the zfs kernel module.

ARC cache memory usage will vary depending on zfs pool sizes. I've had a 50TB single vdev raidz2 pool consume 24GB of memory at system idle when unlimted however zfs wll generally default to using 50% of available system memory for the ARC cache

(Temporary) Change the ARC max for the running system to 4 GB

root #echo 4294967296 >> /sys/module/zfs/parameters/zfs_arc_max

(Permanent) Save the 4 GB ARC cap as a loadable kernel parameter

root #echo "options zfs zfs_arc_max=4294967296" >> /etc/modprobe.d/zfs.conf

Once we have the above file created, let's regenerate the initramfs. genkernel will automatically detect that this file exists and copy it into the initramfs. When you reboot your machine, the initramfs will load up the zfs kernel module with the parameters found in the file.

root #dracut --hostonly -k /lib/modules/5.4.92-gentoo/ --kver 5.4.92-gentoo -f /boot/initramfs-5.4.92-gentoo.img
root #mount /efi
root #cd /efi/efi/gentoo
root #cp /boot/initramfs-5.4.92-gentoo.img .
root #cd
root #umount /efi

Limiting maximum trim I/Os active to each device. ( Optional )

Some hard disk controllers or ssd disks may exhibit disk controller resets when zpool trim <poolname> is run due to either the disk controller or disk not being able to process multiple synchronous disk controller driver commands being issued to a disk.

A known workaround is to reduce the default value of zfs_vdev_trim_max_active from the default value of 2 to 1 using a zfs driver parameter in the /etc/modprobe.d/zfs.conf file, and then remake your initramfs. When the system starts up, and the module is loaded, these options will be passed to the zfs kernel module.

I've had this behavior or symptom occur using an LSI 9305-16i HBA controller which relies on the mpt3sas kernel driver with Samsung 860 evo ssd's.

There is an open bug on openzfs git discussing this issue.

If this symptom did occur and a sysadmin had zpool trim configured to run from a crontab schedule a zfs pool scrub may be required, pool desync or data corruption at the very worst may occur. zfs has always detected the controller reset behavior as the pool or disk within the pool having been affected by an unrecoverable error prompting zpool replace to be used or zpool clear to clear the error state.

(Temporary) Change maximum trim I/Os active to each device.

root #echo 1 > /sys/module/zfs/parameters/zfs_vdev_trim_max_active

(Permanent) Save the maximum trim I/Os active to each device as a loadable kernel parameter

root #echo "options zfs zfs_vdev_trim_max_active=1" >> /etc/modprobe.d/zfs.conf

Once we have the above file created, let's regenerate the initramfs. genkernel will automatically detect that this file exists and copy it into the initramfs. When you reboot your machine, the initramfs will load up the zfs kernel module with the parameters found in the file.

root #dracut --hostonly -k /lib/modules/5.4.92-gentoo/ --kver 5.4.92-gentoo -f /boot/initramfs-5.4.92-gentoo.img
root #mount /efi
root #cd /efi/efi/gentoo
root #cp /boot/initramfs-5.4.92-gentoo.img .
root #cd
root #umount /efi

Successful Installations

Credit and Thanks