New Sheet Added: MDADM (Linux RAID)

cheat/cheatsheets/mdadm

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+# For the sake of briefness, we use Bash  "group compound" stanza:
+#   /dev/sd{a,b,...}1 => /dev/sda1 /dev/sdb1 ...
+# Along the following variables:
+#   ${M} array identifier (/dev/md${M})
+#   ${D} device identifier (/dev/sd${D})
+#   ${P} partition identifier (/dev/sd${D}${P})
+
+# Create (initialize) a new array
+mdadm --create /dev/md${M} --level=raid5 --raid-devices=4 /dev/sd{a,b,c,d,e}${P} --spare-devices=/dev/sdf1
+
+# Manually assemble (activate) an existing array
+mdadm --assemble /dev/md${M} /dev/sd{a,b,c,d,e}${P}
+
+# Automatically assemble (activate) all existing arrays
+mdadm --assemble --scan
+
+# Stop an assembled (active) array
+mdadm --stop /dev/md${M}
+
+# See array configuration
+mdadm --query /dev/md${M}
+
+# See array component configuration (dump superblock content)
+mdadm --query --examine /dev/sd${D}${P}
+
+# See detailed array confiration/status
+mdadm --detail /dev/md${M}
+
+# Save existing arrays configuration
+# (MAY be required by initrd for successfull boot)
+mdadm --detail --scan > /etc/mdadm/mdadm.conf
+
+# Erase array component superblock
+# (MUST do before reusing a partition for other purposes)
+mdadm --zero-superblock /dev/sd${D}${P}
+
+# Manually mark a component as failed
+# (SHOULD when a device shows wear-and-tear signs, e.g. through SMART)
+mdadm --manage /dev/md${M} --fail /dev/sd${D}${P}
+
+# Remove a failed component
+# (SHOULD before preemptively replacing a device, after failing it)
+mdadm --manage /dev/md${M} --remove /dev/sd${D}${P}
+
+# Prepare (format) a new device to replace a failed one
+sfdisk -d /dev/sd${D,sane} | sfdisk /dev/sd${D,new}
+
+# Add new component to an existing array
+# (this will trigger the rebuild)
+mdadm --manage /dev/md${M} --add /dev/sd${D,new}${P}
+
+# See assembled (active) arrays status
+cat /proc/mdstat
+
+# Rename a device
+# (SHOULD after hostname change; eg. name="$(hostname -s)")
+mdadm --assemble /dev/md${M} /dev/sd{a,b,c,d,e}${P} --name="${name}:${M}" --update=name
+