====== Mdadm Helpers ======

*************

===== Debian Disable/Enable Raid Monthly Checks =====

<code>dpkg-reconfigure mdadm</code>

or edit cron job

<code>nano /etc/cron.d/mdadm</code>

[[https://askubuntu.com/questions/1304738/mdadm-checking-raid-5-array-after-each-restart|External Link]]



===== How do I replace a disk marked as removed from a linux md raid-5 array =====

== If drives are "hot swap", don't need to power off server/pc...  ==


First identify removed drive:
 <code>lsblk</code>
Find serial number, if necessary:
<code>smartctl -a /dev/sdb | grep Serial</code>

If drive is **just remved**:
<code>mdadm --zero-superblock /dev/sdXn
mdadm /dev/md0 --add /dev/sdXn</code>

 If **replacing damaged** drive, then only:
<code>mdadm /dev/md0 --add /dev/sdXn</code>
=== Check every drive manually ===

<code>mdadm --examine /dev/sdX</code>

====== “not enough to start the array” – error while staring mdadm RAID array ======

Stop failed array:
<code>mdadm -S /dev/md0</code>

 Assemble the pre-existing array:
<code>mdadm -A -f /dev/md0</code>

====== Test Email Settings ======

<code>mdadm --monitor --scan --test</code>

If got error: **"mdadm: Only one autorebuild process allowed in scan mode, aborting"**
<code>mdadm --monitor /dev/md0 --test</code>



====== Simple Script to read Hdd serial numbers ======

<code>#!/bin/bash
smartctl -a /dev/sda | grep -i 'Serial';
echo "";
echo "";

for i in {a..z} ; do
echo $i
smartctl -a /dev/sd$i | grep -i 'Serial';
done
</code>

====== A SparesMissing event had been detected on md device ======

Removing the spares=1 option or just recreating the mdadm.conf from scratch fixes the problem:

====== **Update MDADM config file** ======


<code>/usr/share/mdadm/mkconf > /etc/mdadm/mdadm.conf.copy</code>

Double check new configuration ad then save as mdadm.conf

====== **Just in case** ======

Run <code>update-initramfs -u</code>
====== Speed Up or Slow Down Raid rebuild ======

To see current limits, enter:

<code>sysctl dev.raid.speed_limit_min
sysctl dev.raid.speed_limit_max</code>


To change minimal speed (ex. min.= 10000), enter:

<code>echo value > /proc/sys/dev/raid/speed_limit_min</code>

or 
<code>sysctl -w dev.raid.speed_limit_min=value</code>

To change maximal speed (ex. max.= 200000), enter:

<code>echo value > /proc/sys/dev/raid/speed_limit_max</code>

or 
<code>sysctl -w dev.raid.speed_limit_max=value</code>


If you want to override the defaults you could add these two lines to: <code>nano /etc/sysctl.conf</code>

<code>#################NOTE ################
##  You are limited by CPU and memory too #
###########################################
dev.raid.speed_limit_min = 50000
## good for 4-5 disks based array ##
dev.raid.speed_limit_max = 2000000
## good for large 6-12 disks based array ###
dev.raid.speed_limit_max = 5000000</code>

Source: [[https://www.cyberciti.biz/tips/linux-raid-increase-resync-rebuild-speed.html|External Link]]



===== Speed Change Script Example =====


<code>
#!/bin/bash
clear;
speed=$(cat /proc/sys/dev/raid/speed_limit_max)
echo ""
echo -e "\e[92m *\e[0m Speed Was: \e[92m$speed\e[0m"
echo ""
echo -e "\e[92m *\e[0m Switching to:\e[0m"
tput setaf 2
tput bold
if [[ $speed == '150000' ]]; then
    sysctl -w dev.raid.speed_limit_max=10000 | cut -c 28- | sed  -e   's/^/                 /'
    sysctl -w dev.raid.speed_limit_min=1000  | cut -c 28- | sed  -e   's/^/                 /'
else
    sysctl -w dev.raid.speed_limit_max=150000 | cut -c 28- | sed  -e 's/^/                 /'
    sysctl -w dev.raid.speed_limit_min=10000  | cut -c 28- | sed  -e   's/^/                 /'
fi

tput sgr0
</code>