Software RAID on Linux is a snap.doc
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Software RAID on Linux is a snap, thanks to the mdadm tool that comes
with most modern Linux distributions. Software RAID, particularly RAID1,
is an inexpensive way to create instant backups and protect your systems
against data loss in the event that one drive fails.
To create a RAID device, execute the following command:
# mdadm --create --verbose /dev/md0 --level=1
--raid-devices=2 \
/dev/hda1 /dev/hdc1
There are two ways to obtain information about the RAID array. You can
query the device with mdadm, which provides detailed information on a
particular device, or you can get an overview of the entire RAID system by
looking at /proc/mdstat directly. For example:
# cat /proc/mdstat
Personalities : [raid1]
read_ahead 1024 sectors
md0 : active raid1 hda1[0] hdc1[1]
56261376 blocks [2/2] [UU]
Here you can see that the personality is RAID1, the device /dev/md0 is
active, and both disks are active (noted by [UU]). To obtain more detailed
information about this device, use the following command:
# mdadm --detail /dev/md0
This will print out a variety of information about the device, including when
it was created, its size, and the time it was last updated.
If you want to change drives, you can remove a device from the array. This
command will prevent the partition /dev/hdc1 from appearing in the
/dev/md0 array:
# mdadm /dev/md0 -r /dev/hdc1
You can also add the device back into the array. Here's how:
# mdadm /dev/md0 -a /dev/hdc1
