Tag: raid1

Inactive array – mdadm: Cannot get array info for /dev/md126

Replacing a disk maybe sometimes challenging, especially with software RAID. If the software RAID1 went inactive this article might be for you!
Booting from a LIVECD or a rescue PXE system and all RAID devices got inactive despite the loaded personalities. We have similar article on the subject – Recovering MD array and mdadm: Cannot get array info for /dev/md0

livecd ~ # cat /proc/mdstat 
Personalities : [raid6] [raid5] [raid4] [raid0] [raid1] [raid10] [linear] [multipath] 
md125 : inactive sdb3[1](S)
      1047552 blocks super 1.2
       
md126 : inactive sdb1[1](S)
      52427776 blocks super 1.2
       
md127 : inactive sdb2[1](S)
      16515072 blocks super 1.2
       
unused devices: <none>

Despite the personalities are loaded, which means the kernel modules are successfully loaded – “[raid6] [raid5] [raid4] [raid0] [raid1] [raid10] [linear] [multipath] “. Still, something got wrong and the device’s personality is unrecognized and is inactive state.
A device in inactive state cannot be recovered and it cannot be added disks:

livecd ~ # mdadm --add /dev/md125 /dev/sda3
mdadm: Cannot get array info for /dev/md125

In general, to recover a RAID in inactive state:

  1. Check if the kernel modules are loaded. If the RAID setups are using RAID1, the “Personalities” line in /proc/mdstat should include it as “[raid1]”
  2. Try to run the device with “mdadm –run”
  3. Add the missing device to the RAID device with “mdadm –add” if the status of the RAID device goes to “active (auto-read-only)” or just “active”.
  4. Wait for the RAID device to recover.

Keep on reading!

Remove disk (all partitions) from software RAID1 with mdadm and change layout of the disk

The following article is to show how to remove healthy partitions from software RAID1 devices to change the layout of the disk and then add them back to the array.
The mdadm is the tool to manipulate the software RAID devices under Linux and it is part of all Linux distributions (some don’t install it by default so it may need to be installed).

Software RAID layout

[root@srv ~]# cat /proc/mdstat 
Personalities : [raid1] 
md125 : active raid1 sda4[1] sdb3[0]
      1047552 blocks super 1.2 [2/2] [UU]
      bitmap: 0/1 pages [0KB], 65536KB chunk

md126 : active raid1 sdb2[0] sda3[1]
      32867328 blocks super 1.2 [2/2] [UU]
      
md127 : active raid1 sda2[1] sdb1[0]
      52427776 blocks super 1.2 [2/2] [UU]
      bitmap: 0/1 pages [0KB], 65536KB chunk

unused devices: <none>

STEP 1) Make the partitions faulty.

The partitions cannot be removed if they are not faulty.

[root@srv ~]# mdadm --fail /dev/md125 /dev/sdb3
mdadm: set /dev/sdb3 faulty in /dev/md125
[root@srv ~]# mdadm --fail /dev/md126 /dev/sdb2
mdadm: set /dev/sdb2 faulty in /dev/md126
[root@srv ~]# mdadm --fail /dev/md127 /dev/sdb1
mdadm: set /dev/sdb1 faulty in /dev/md127

Keep on reading!

CentOS 8 dracut-initqueue timeout and could not boot – warning /dev/disk/by-id/md-uuid- does not exist – inactive raids

Booting the CentOS 8 failed with

dracut-initqueue timeout and could not boot – warning /dev/disk/by-id/md-uuid- does not exist

we have an article on the subject for CentOS 7 – CentOS 7 dracut-initqueue timeout and could not boot – warning /dev/disk/by-id/md-uuid- does not exist and we continue with another issue with the same error.
Most times when you get this error there is a mistake in some UUID for the file system or the RAID devices. But this time our software raid was autodetected with the right disks but it ended in INACTIVE STATE. Software raid in INACTIVE STATE cannot be used so we are in “Emergency mode”:

SCREENSHOT 1) Without root partition the boot process enters the dracut emergency mode.

main menu
Entering emergency mode

SCREENSHOT 2) Software md raid device information – missing “Personalities” for the raid groups.

Loaded modules in the kernel and missing raid kernel modules.

main menu
Missing raid1 kernel module in initram file

To summarize it up:

  • The disks are detected, so we drivers for SATA/SAS controller is loaded correctly.
  • The software raid autodetected the MD devices, but they are in “INACTIVE STATE”. The RAID “Personalities” is missing.

Keep on reading!

SSD cache device to a software raid using LVM2

Inspired by our article – SSD cache device to a hard disk drive using LVM, which uses SSD driver as a cache device to a single hard drive, we decided to make a new article, but this time using two hard drives in raid setup (in our case RAID1 for redundancy) and a single NVME SSD drive.
The goal:
Caching RAID1 consisting of two 8T hard drive with a single 1T NVME SSD drive. Caching reads and writes, i.e. the write-back is enabled.
Our setup:

  • 1 NVME SSD disk Samsung 1T. It will be used for writeback cache device (you may use writethrough, too, to maintain the redundancy of the whole storage)!
  • 2 Hard disk drive 8T grouped in RAID1 for redundancy.

STEP 1) Install lvm2 and enable the lvm2 service

Only this step is different on different Linux distributions. We included three of them:
Ubuntu 16+:

sudo apt update && apt upgrade -y
sudo apt install lvm2 -y
systemctl enable lvm2-lvmetad
systemctl start lvm2-lvmetad

CentOS 7:

yum update
yum install -y lvm2
systemctl enable lvm2-lvmetad
systemctl start lvm2-lvmetad

Gentoo:

emerge --sync
emerge -v sys-fs/lvm2
/etc/init.d/lvm start
rc-update add default lvm

Keep on reading!