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ZFS as Root Filesystem
Introduction
This tutorial will show you how to install Funtoo on ZFS (rootfs). This tutorial is meant to be an "overlay" over the Regular Funtoo Installation. Follow the normal installation and only use this guide for steps 2, 3, and 8.
Introduction to ZFS
Since ZFS is a new technology for Linux, it can be helpful to understand some of its benefits, particularly in comparison to BTRFS, another popular next-generation Linux filesystem:
- On Linux, the ZFS code can be updated independently of the kernel to obtain the latest fixes. btrfs is exclusive to Linux and you need to build the latest kernel sources to get the latest fixes.
- ZFS is supported on multiple platforms. The platforms with the best support are Solaris, FreeBSD and Linux. Other platforms with varying degrees of support are NetBSD, Mac OS X and Windows. btrfs is exclusive to Linux.
- ZFS has the Adaptive Replacement Cache replacement algorithm while btrfs uses the Linux kernel's Last Recently Used replacement algorithm. The former often has an overwhelmingly superior hit rate, which means fewer disk accesses.
- ZFS has the ZFS Intent Log and SLOG devices, which accelerates small synchronous write performance.
- ZFS handles internal fragmentation gracefully, such that you can fill it until 100%. Internal fragmentation in btrfs can make btrfs think it is full at 10%. Btrfs has no automatic rebalancing code, so it requires a manual rebalance to correct it.
- ZFS has raidz, which is like RAID 5/6 (or a hypothetical RAID 7 that supports 3 parity disks), except it does not suffer from the RAID write hole issue thanks to its use of CoW and a variable stripe size. btrfs gained integrated RAID 5/6 functionality in Linux 3.9. However, its implementation uses a stripe cache that can only partially mitigate the effect of the RAID write hole.
- ZFS send/receive implementation supports incremental update when doing backups. btrfs' send/receive implementation requires sending the entire snapshot.
- ZFS supports data deduplication, which is a memory hog and only works well for specialized workloads. btrfs has no equivalent.
- ZFS datasets have a hierarchical namespace while btrfs subvolumes have a flat namespace.
- ZFS has the ability to create virtual block devices called zvols in its namespace. btrfs has no equivalent and must rely on the loop device for this functionality, which is cumbersome.
The only area where btrfs is ahead of ZFS is in the area of small file efficiency. btrfs supports a feature called block suballocation, which enables it to store small files far more efficiently than ZFS. It is possible to use another filesystem (e.g. reiserfs) on top of a ZFS zvol to obtain similar benefits (with arguably better data integrity) when dealing with many small files (e.g. the portage tree).
For a quick tour of ZFS and have a big picture of its common operations you can consult the page ZFS Fun.
Disclaimers
This guide is a work in progress. Expect some quirks.
Some tests showed that the kernel build and grub installation is working when using somehow the basic line from: https://github.com/ryao/zfs-overlay/blob/master/zfs-install.
The guide will be changed accordingly in the next days...
Since ZFS was really designed for 64 bit systems, we are only recommending and supporting 64 bit platforms and installations. We will not be supporting 32 bit platforms!
Downloading the ISO (With ZFS)
In order for us to install Funtoo on ZFS, you will need an environment that already provides the ZFS tools. Therefore we will download a customized version of System Rescue CD with ZFS included.
Name: sysresccd-4.2.0_zfs_0.6.2.iso (545 MB) Release Date: 2014-02-25 md5sum 01f4e6929247d54db77ab7be4d156d85
Download System Rescue CD with ZFS
Creating a bootable USB from ISO (From a Linux Environment)
After you download the iso, you can do the following steps to create a bootable USB:
Make a temporary directory root # mkdir /tmp/loop Mount the iso root # mount -o ro,loop /root/sysresccd-4.2.0_zfs_0.6.2.iso /tmp/loop Run the usb installer root # /tmp/loop/usb_inst.sh
That should be all you need to do to get your flash drive working.
Booting the ISO
When booting into the ISO, Make sure that you select the "Alternate 64 bit kernel (altker64)". The ZFS modules have been built specifically for this kernel rather than the standard kernel. If you select a different kernel, you will get a fail to load module stack error message.
Creating partitions
There are two ways to partition your disk: You can use your entire drive and let ZFS automatically partition it for you, or you can do it manually.
We will be showing you how to partition it manually because if you partition it manually you get to create your own layout, you get to have your own separate /boot partition (Which is nice since not every bootloader supports booting from ZFS pools), and you get to boot into RAID10, RAID5 (RAIDZ) pools and any other layouts due to you having a separate /boot partition.
gdisk (GPT Style)
A Fresh Start:
First lets make sure that the disk is completely wiped from any previous disk labels and partitions.
We will also assume that /dev/sda is the target drive.
root # sgdisk -Z /dev/sda
This is a destructive operation and the program will not ask you for confirmation! Make sure you really don't want anything on this disk.
Now that we have a clean drive, we will create the new layout.
First open up the application:
root # gdisk /dev/sda
Create Partition 1 (boot):
Command: n ↵ Partition Number: ↵ First sector: ↵ Last sector: +250M ↵ Hex Code: ↵
Create Partition 2 (BIOS Boot Partition):
Command: n ↵ Partition Number: ↵ First sector: ↵ Last sector: +32M ↵ Hex Code: EF02 ↵
Create Partition 3 (ZFS):
Command: n ↵ Partition Number: ↵ First sector: ↵ Last sector: ↵ Hex Code: bf00 ↵ Command: p ↵ Number Start (sector) End (sector) Size Code Name 1 2048 514047 250.0 MiB 8300 Linux filesystem 2 514048 579583 32.0 MiB EF02 BIOS boot partition 3 579584 1953525134 931.2 GiB BF00 Solaris root Command: w ↵
Format your /boot partition
root # mkfs.ext2 -m 1 /dev/sda1
Create the zpool
We will first create the pool. The pool will be named tank. Feel free to name your pool as you want. We will use ashift=12 option which is used for a hard drives with a 4096 sector size.
root # zpool create -f -o ashift=12 -o cachefile=/tmp/zpool.cache -O normalization=formD -m none -R /mnt/funtoo tank /dev/sda3
Create the zfs datasets
We will now create some datasets. For this installation, we will create a small but future proof amount of datasets. We will have a dataset for the OS (/), and your swap. We will also show you how to create some optional datasets as examples ones: /home, /usr/src, and /usr/portage.
Create some empty containers for organization purposes, and make the dataset that will hold / root # zfs create -p tank/funtoo root # zfs create -o mountpoint=/ tank/funtoo/root Optional, but recommended datasets: /home root # zfs create -o mountpoint=/home tank/funtoo/home Optional datasets: /usr/src, /usr/portage/{distfiles,packages} root # zfs create -o mountpoint=/usr/src tank/funtoo/src root # zfs create -o mountpoint=/usr/portage -o compression=off tank/funtoo/portage root # zfs create -o mountpoint=/usr/portage/distfiles tank/funtoo/portage/distfiles root # zfs create -o mountpoint=/usr/portage/packages tank/funtoo/portage/packages
Installing Funtoo
Pre-Chroot
Go into the directory that you will chroot into root # cd /mnt/funtoo Make a boot folder and mount your boot drive root # mkdir boot root # mount /dev/sda1 boot
Now download and extract the Funtoo stage3 ...
It is trully recommended to use the current version and generic64. That reduces the risk of a broken build.
After successfull ZFS installation and successfull first boot, the kernel may be changed using the eselect profile set ... command. If you create a snapshot before, you may allways come back to your previous installation, with some simple steps ... (rollback your pool and in the worst case configure and install the bootloader again)
Once you've extracted the stage3, do a few more preparations and chroot into your new funtoo environment:
Bind the kernel related directories root # mount -t proc none proc root # mount --rbind /dev dev root # mount --rbind /sys sys Copy network settings root # cp -f /etc/resolv.conf etc Make the zfs folder in 'etc' and copy your zpool.cache root # mkdir etc/zfs root # cp /tmp/zpool.cache etc/zfs Chroot into Funtoo root # env -i HOME=/root TERM=$TERM chroot . bash -l
How to create zpool.cache file?
If no zpool.cache file is available, the following command will create one:
root # zpool set cachefile=/etc/zfs/zpool.cache tank
Add filesystems to /etc/fstab
Before we continue to compile and or install our kernel in the next step, we will edit the /etc/fstab file because if we decide to install our kernel through portage, portage will need to know where our /boot is, so that it can place the files in there.
Edit /etc/fstab:
/etc/fstab # <fs> <mountpoint> <type> <opts> <dump/pass>
/dev/sda1 /boot ext2 defaults 0 2
Initial kernel build before emerging zfs
Install genkernel using:
root # emerge genkernel Build initial kernel (required for checks in sys-kernel/spl and sys-fs/zfs): root # genkernel kernel --no-clean --no-mount-boot
Installing the ZFS userspace tools and kernel modules
Emerge No results. This package will bring in No results, and No results as its dependencies:
root # emerge zfs
Check to make sure that the zfs tools are working. The zpool.cache file that you copied before should be displayed.
root # zpool status root # zfs list
If everything worked, continue.
Create kernel and initramfs
initial kernel build
Install genkernel using:
root # emerge genkernel Build initial kernel (required for checks in sys-kernel/spl and sys-fs/zfs): root # genkernel kernel --no-clean --no-mount-boot
Installing & Configuring the Bootloader
GRUB 2
root # emerge grub
Now install grub to the drive itself (not a partition):
root # grub-install /dev/sda
boot-update
boot-update comes as a dependency of grub2, so if you already installed grub, it's already on your system!
Genkernel
If your using genkernel you must add 'real_root=ZFS=<root>' and 'dozfs' to your params.
Example entry for /etc/boot.conf:
/etc/boot.conf "Funtoo ZFS" {
kernel kernel[-v]
initrd initramfs-genkernel-x86_64[-v]
params real_root=ZFS=tank/funtoo/root
params += dozfs=force
}
After editing /etc/boot.conf, you just need to run boot-update to update grub.cfg
root # boot-update
If boou-updatefails, try this:
root # grub-mkconfig -o /boot/grub/grub.cfg
Final configuration
Add the zfs tools to openrc
root # rc-update add zfs boot
Clean up and reboot
We are almost done, we are just going to clean up, set our root password, and unmount whatever we mounted and get out.
Delete the stage3 tarball that you downloaded earlier so it doesn't take up space. root # cd / root # rm stage3-latest.tar.xz Set your root password root # passwd >> Enter your password, you won't see what you are writing (for security reasons), but it is there! Get out of the chroot environment root # exit Unmount all the kernel filesystem stuff and boot (if you have a separate /boot) root # umount -l proc dev sys boot Turn off the swap root # swapoff /dev/zvol/tank/swap Export the zpool root # cd / root # zpool export tank Reboot root # reboot
Don't forget to set your root password as stated above before exiting chroot and rebooting. If you don't set the root password, you won't be able to log into your new system.
and that should be enough to get your system to boot on ZFS.
After reboot
Forgot to reset password?
System Rescue CD
If you aren't using bliss-initramfs, then you can reboot back into your sysresccd and reset through there by mounting your drive, chrooting, and then typing passwd.
Example:
root # zpool import -f -R /mnt/funtoo tank root # chroot /mnt/funtoo bash -l root # passwd root # exit root # zpool export -f tank root # reboot
Create initial ZFS Snapshot
Continue to set up anything you need in terms of /etc configurations. Once you have everything the way you like it, take a snapshot of your system. You will be using this snapshot to revert back to this state if anything ever happens to your system down the road. The snapshots are cheap, and almost instant.
To take the snapshot of your system, type the following:
root # zfs snapshot -r tank@install
To see if your snapshot was taken, type:
root # zfs list -t snapshot
If your machine ever fails and you need to get back to this state, just type (This will only revert your / dataset while keeping the rest of your data intact):
root # zfs rollback tank/funtoo/root@install
For a detailed overview, presentation of ZFS' capabilities, as well as usage examples, please refer to the ZFS Fun page.
Troubleshooting
Starting from scratch
If your installation has gotten screwed up for whatever reason and you need a fresh restart, you can do the following from sysresccd to start fresh:
Destroy the pool and any snapshots and datasets it has root # zpool destroy -R -f tank This deletes the files from /dev/sda1 so that even after we zap, recreating the drive in the exact sector position and size will not give us access to the old files in this partition. root # mkfs.ext2 /dev/sda1 root # sgdisk -Z /dev/sda
Now start the guide again :).
Starting again reusing the same disk partitions and the same pool
If your installation has gotten screwed up for whatever reason and you want to keep your pole named tank than you should boou into the Rescue CD / USB as done before.
import the pool reusing all existing datasets: root # zpool import -f -R /mnt/funtoo tank
Now you should wipe the previous installation off:
let's go to our base installation directory: root # cd /mnt/funtoo and delete the old installation: root # rm -rf *
Now start the guide again, at "Pre-Chroot"