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comparison content/Linux/software-raid-setup.md @ 85:2444e4533089
add the RAID setup article
| author | Dirk Olmes <dirk@xanthippe.ping.de> |
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| date | Wed, 12 Jul 2017 04:14:55 +0200 |
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| children | abc2401e9958 |
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| 1 Title: Setting up a software RAID1 | |
| 2 Date: 2017-07-12 | |
| 3 Lang: en | |
| 4 Tags: Gentoo | |
| 5 | |
| 6 I'm helping a friend to set up a machine with [Gentoo](http://www.gentoo.org). This will be a machine to host production applications and it is equipped with 2 identical hard drives. I will set up a [software RAID 1](https://raid.wiki.kernel.org). This has been a life saver on a similar machine before where one of the drives failed and we had no data loss and only minimal downtime during which the drive was replaced. | |
| 7 | |
| 8 One goal of the new setup is to remain bootable even if one of the drives fails. I had trouble accomplishing this in earlier setups so this time I tested the process locally on a virtual machine before setting up the real iron. | |
| 9 | |
| 10 The first step of the setup is partitioning the drives. The [handbook](https://wiki.gentoo.org/wiki/Handbook:AMD64/Installation/Disks) suggests adding a small partition at the beginning of the drive to enabl booting from a gpt partitioned drive. The `/boot` partition will be formatted using [ext4](https://en.wikipedia.org/wiki/Ext4) because the filesystem will remain bootable even if one of the drives is missing. The rest of the disk will be formatted using [xfs](https://en.wikipedia.org/wiki/XFS). To recap the layout: | |
| 11 | |
| 12 Number Start End Size File system Name Flags | |
| 13 1 1.00MiB 3.00MiB 2.00MiB grub bios_grub | |
| 14 2 3.00MiB 95.0MiB 92.0MiB boot | |
| 15 3 95.0MiB 8191MiB 8096MiB rootfs raid | |
| 16 | |
| 17 The second drive is partitioned exactly the same. | |
| 18 | |
| 19 Now let's create a RAID 1 for the boot partition: | |
| 20 | |
| 21 mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb2 /dev/sdc2 | |
| 22 | |
| 23 and for the rootfs: | |
| 24 | |
| 25 mdadm --create /dev/md1 --level=1 --raid-devices=2 /dev/sdb3 /dev/sdc3 | |
| 26 | |
| 27 To maintain the RAID device numbering even after reboot, the RAID config has to be saved. This will be done by | |
| 28 | |
| 29 mdadm --detail --scan >> /etc/mdadm.conf | |
| 30 | |
| 31 Then create an ext4 filesystem on `/dev/md0` and an xfs filesystem on `/dev/md1`. Nothing noteworthy here. | |
| 32 | |
| 33 The observant reader will have noticed from the device names above that I'm testing my installation from a running system on `/dev/sda`. To save the hassle of going through the entire stage3 setup process I'm simply copying the running system to the newly created RAID filesystems. | |
| 34 | |
| 35 After chrooting into the new system some changes have to be made to the [genkernel](https://wiki.gentoo.org/wiki/Genkernel) config in order to produce a RAID enabled initramfs. In `/etc/genkernel.conf` set | |
| 36 | |
| 37 MDADM="yes" | |
| 38 MDADM_CONFIG="/etc/mdadm.conf" | |
| 39 | |
| 40 Now we're set to build the kernel. | |
| 41 | |
| 42 While it's compiling, edit `/etc/default/grub` (I'm of course using [grub2](https://www.gnu.org/software/grub/manual/grub.html) for booting) and add | |
| 43 | |
| 44 GRUB_CMDLINE_LINUX="domdadm" | |
| 45 | |
| 46 Setup grub on both devices individually using `grub-install /dev/sdb` and `grub-install /dev/sdc`. | |
| 47 | |
| 48 After the kernel has finished compiling, generate the proper grub config using `grub-mkconfig -o /boot/grub/grub.cfg`. | |
| 49 | |
| 50 Before rebooting the `fstab` has to be set up correctly. I prefer to use UUIDs for filesystems instead of device names - this is a bit more fault tolerant in case device numbering is mixed up. It was a main challenge to find an unambiguous UUID for the both RAID filesystems. There are a number of places to get a UUID from: `mdadm --detail`, `blkid`, `tune2fs -l`, `xfs_admin -u` and I'm sure I forgot more. The helpful guys at the [gentoo IRC channel](https://www.gentoo.org/get-involved/irc-channels/) pointed me in the right direction. Use `lsblk -f /dev/md0` to find a UUID that uniquely identifies the RAID and check using `findfs UUID=<uuid>`. | |
| 51 | |
| 52 After updating the `fstab` the system is ready for a first boot into the RAID setup. | |
| 53 | |
| 54 I tested failing drives by simply removing the first (or the second) drive from the virtual machine. The whole setup still boots off either drive. |