There are a few options for software RAID on Gnu Linux. Among them is BtrFS and ZFS (the latter of which has licensing issues, so use discretion before using)., however today I will focus on mdadm. This is historically the oldest software raid, therefore should be better vetted, although its performance may be less of that of the first two mentioned - for simple servers, mdadm might be the most stable choice.
Creation of RAID
Will not be covered here (yet). You must create the partition tables. Create the raid with mdadm. mkfs.ext4 on the raid partition. Add mdadm to grub config. Reinstall grub. Details may be provided later.
Status / Details
# sudo mdadm -D /dev/md127
/dev/md127: Version : 1.2 Creation Time : Fri Feb 1 01:00:25 2019 Raid Level : raid1 Array Size : 57638912 (54.97 GiB 59.02 GB) Used Dev Size : 57638912 (54.97 GiB 59.02 GB) Raid Devices : 3 Total Devices : 2 Persistence : Superblock is persistent Update Time : Fri Feb 1 02:40:44 2019 State : clean, degraded Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 Name : devuan:root UUID : 83a8dc03:802a4129:26322116:c2cfe1d4 Events : 82 Number Major Minor RaidDevice State - 0 0 0 removed 1 8 17 1 active sync /dev/sdb1 2 8 33 2 active sync /dev/sdc1
(here you can see, one was removed. It auto removes, when unplugged)
Add Drive to Array
This assumes you have already created the RAID. This is for adding to an existing array.
# mdadm --add /dev/md127 /dev/sda1
NOTE: If you setup 2 hdds, in a raid, and want to add a third, if you just --add, it will show up as a spare...
if you do mdadm --grow /dev/md127 -raid-devices=3 then the third might be active sync (what we want) note that the --grow, seems to allow for parameter changes after you have already created the raid. you can also specify the exact same command, raid-devices=3 in the setup of the raid (see install doc). Note that if you lose a drive, you can simply add it.
NOTE: don't worry about mkfs.ext4 on the raid members, after initial setup. The RAID will manage that.
NOTE: if you have a new drive and need to copy the hdd partition tables: https://unix.stackexchange.com/questions/12986/how-to-copy-the-partition-layout-of-a-whole-disk-using-standard-tools or aka
(FOR MBR ONLY) Save: sfdisk -d /dev/sda > part_table Restore: sfdisk /dev/NEWHDD < part_table (FOR GPT:) # Save MBR disks sgdisk --backup=/partitions-backup-$(basename $source).sgdisk $source sgdisk --backup=/partitions-backup-$(basename $dest).sgdisk $dest # Copy $source layout to $dest and regenerate GUIDs sgdisk --replicate=$dest $source sgdisk -G $dest
Add HDD back to RAID (to fix failed drive)
# mdadm --add /dev/md127 /dev/sda1 mdadm: added /dev/sda1 # sudo mdadm -D /dev/md127 /dev/md127: Version : 1.2 Creation Time : Fri Feb 1 01:00:25 2019 Raid Level : raid1 Array Size : 57638912 (54.97 GiB 59.02 GB) Used Dev Size : 57638912 (54.97 GiB 59.02 GB) Raid Devices : 3 Total Devices : 3 Persistence : Superblock is persistent Update Time : Fri Feb 1 02:41:43 2019 State : clean, degraded, recovering Active Devices : 2 Working Devices : 3 Failed Devices : 0 Spare Devices : 1 Rebuild Status : 0% complete Name : devuan:root UUID : 83a8dc03:802a4129:26322116:c2cfe1d4 Events : 92 Number Major Minor RaidDevice State 3 8 1 0 spare rebuilding /dev/sda1 1 8 17 1 active sync /dev/sdb1 2 8 33 2 active sync /dev/sdc1
You can check on the rebuild partway:
Rebuild Status : 6% complete Name : devuan:root UUID : 83a8dc03:802a4129:26322116:c2cfe1d4 Events : 103 Number Major Minor RaidDevice State 3 8 1 0 spare rebuilding /dev/sda1 1 8 17 1 active sync /dev/sdb1 2 8 33 2 active sync /dev/sdc1
You can also watch it via /proc/
watch -n1 cat /proc/mdstat
Every 1.0s: cat /proc/mdstat server: Fri Feb 1 02:43:24 2019 Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10] md127 : active raid1 sda1 sdb1 sdc1 57638912 blocks super 1.2 [3/2] [_UU] [==>..................] recovery = 11.2% (6471936/57638912) finish=13.2min speed=64324K/sec unused devices: <none>
WARNING: Reinstall grub on the new drive again as well afterwards.
Test emails on mdadm.. first configure email however you prefer (i currently use ssmtp).
edit /etc/mdadm/mdadm.conf; put the email recipient in mailadd variable
# mdadm --monitor --scan --test --oneshot
should send an email
(Be careful that updates don't break this file. I see it's generated by mkconf.)
https://ubuntuforums.org/showthread.php?t=1185134 for more details on email sending
The section about degraded disks: https://help.ubuntu.com/lts/serverguide/advanced-installation.html.en
General partition tips: https://github.com/zfsonlinux/zfs/wiki/Debian-Stretch-Root-on-ZFS
Configuring Email w/ssmtp: https://wiki.zoneminder.com/SMS_Notifications