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### Configuring and using a software RAID1 (mirroring) with mdadm ### |
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Linux has a really nice support for software RAIDs. The backend tool to manage … |
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*** CREATING THE RAID1 MIRROR *** |
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Creating the RAID1 mirror, using two disks: sdb and sdc: |
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# mdadm --create --verbose /dev/md0 --level=mirror --metadata 1.0 --raid-device… |
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You can also build your RAID-1 with only 1 disk, and add the second one later (… |
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# mdadm --create --verbose /dev/md0 --level=mirror --metadata 1.0 --raid-device… |
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Note that I explicitely asked for an array superblock in version 1.0. This is a… |
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Version 1.0 is stored near the end of the device (at least 8K, and less than 12… |
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You will notice that building the array takes a long time - several hours, or e… |
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# mdadm --grow --bitmap=internal /dev/md0 |
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It's important to keep your mdadm.conf up to date. To do it, use the following … |
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# mdadm --detail --scan > /etc/mdadm/mdadm.conf |
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*** MAKE YOUR RAID BOOTABLE *** |
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If you'd like to make your mdadm array bootable, there are a few details to kno… |
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Apparently you need Grub2 to be able to boot from the RAID (incidentally Grub2 … |
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By default, Grub locates disks using their UUID. This can become messy with RAI… |
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GRUB_DISABLE_LINUX_UUID=true |
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Grub needs a so-called 'device map'. It's basically a text file that provides t… |
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(hd0) /dev/disk/by-id/ata-Hitachi_HDT721010SLA360_STF607MH3VJKBK |
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(hd1) /dev/disk/by-id/ata-ST1000DM003-9YN162_S1DAAY5W |
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(hd2) /dev/md0 |
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EDIT: It would seem that the current (as of 26 Dec 2015) version of Grub2 doesn… |
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Once you're done, you can call the 'update-grub2' command that will recompute a… |
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Example: |
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# grub-install --no-floppy /dev/sda |
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# grub-install --no-floppy /dev/sdb |
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Yes, this IS counter-intuitive, because one would think that doing grub-install… |
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But grub is not the only one involved in the boot process - it will only load a… |
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INITRDSTART='all' |
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...And then, update the initramfs image via 'update-initramfs -u'. Since then, … |
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Last note: Not directly related to RAID, but I wasted a few hours on this. Even… |
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*** DAY TO DAY MANAGEMENT OF THE ARRAY *** |
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How do I check the RAID status? |
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# mdadm --detail /dev/md0 |
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# cat /proc/mdstat |
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How to run a consistency check on the array? |
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# echo check > /sys/block/md0/md/sync_action |
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How to remove a failed drive? This is a two steps process. First mark the drive… |
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# mdadm --manage /dev/md0 --fail /dev/sdb |
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# mdadm --manage /dev/md0 --remove /dev/sdb |
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If you'd like to erase the RAID tag from the drive (for example to avoid Linux … |
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# mdadm --zero-superblock /dev/sdb |
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Adding a new drive into the array: |
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# mdadm --manage /dev/md0 --add /dev/sdb |
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Growing the size of an array after replacing disks with bigger ones: |
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# mdadm --grow /dev/md0 --size=max |
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