## page was renamed from CheatSheet/mdadm

<<TableOfContents>>

== Creation ==

See also [[CheatSheet/Partitioning]].

{{{#!highlight sh numbers=off
# New Linux RAID encompassing the entire disk
sudo sgdisk --largest-new=1 --typecode=fd /dev/disk-dev-device

# RAID 5 array creation
sudo mdadm --create /dev/md5 --level=5 --assume-clean --raid-devices=3 /dev/sd{d,e,f}1

# Create a high-performance RAID10 array (2x read speed compared to RAID1)
sudo mdadm --create /dev/md6 --level=10 -p f2 --assume-clean --raid-devices=2 /dev/sd{i,k}1

# Save configuration (not necessary)
/usr/share/mdadm/mkconf > /new/etc/mdadm/mdadm.conf
}}}

== Performance ==

=== Stripe cache size ===

Increase 1 MiB default to 16 MiB (№ 4K blocks):

{{{#!highlight sh numbers=off
echo 4096 | sudo tee /sys/block/md0/md/stripe_cache_size
echo 4096 | sudo tee /sys/block/md1/md/stripe_cache_size
}}}

=== Write-intent bitmaps ===

[[https://raid.wiki.kernel.org/index.php/Bitmap|Write-intent bitmaps]] speed-up RAID resyncs significantly, at the expense of a little write performance.

{{{#!highlight sh
# Create write-intent bitmap
mdadm --grow --bitmap=internal /dev/mdX

# Remove write-intent bitmap
mdadm --grow --bitmap=none /dev/mdX
}}}

== Diagnosis ==

=== Examine array component ===

Displays superblock information, including last event, RAID UUID, other components, etc.

{{{#!highlight sh numbers=off
mdadm --examine /dev/sda1
}}}

== Recovery ==

=== Inactive array ===

If an array comes out as inactive, e.g.:

{{{
md8 : inactive sdp1[0](S) sds1[4](S) sdx1[2](S) sdj1[1](S)
      7814054094 blocks super 1.2
}}}

Stop the array before we continue to work on it.

{{{#!highlight sh numbers=off
mdadm --stop /dev/md8
}}}

First, use examine the array components and figure out which component is out of sync (it's best to do this manually). Then, with the remaining components, reassemble the array. E.g. if /dev/sds1 was the bad device:

{{{#!highlight sh numbers=off
mdadm --assemble /dev/md8 /dev/sd{p,x,j}1 --force
}}}

to restart the array. If supposedly bad device is fine, go ahead and re-add it:

{{{#!highlight sh numbers=off
mdadm --manage /dev/md8 --add /dev/sds1
}}}

== btrfs ==

{{{#!highlight sh numbers=off
# btrfs RAID0
mkfs.btrfs -d raid0 /dev/sd{b,c}1
}}}

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CategoryCheatSheet