6.3. Managing Software RAID
This section discusses software RAID configuration and management after the installation, and covers the following topics:
- Reviewing existing software RAID configuration.
- Creating a new RAID device.
- Replacing a faulty device in an array.
- Adding a new device to an existing array.
- Deactivating and removing an existing RAID device.
- Saving the configuration.
All examples in this section use the software RAID configuration from the previous section.
6.3.1. Reviewing RAID Configuration
When a software RAID is in use, basic information about all presently active RAID devices are stored in the
/proc/mdstatspecial file. To list these devices, display the content of this file by typing the following at a shell prompt:
To determine whether a certain device is a RAID device or a component device, run the command in the following form as
In order to examine a RAID device in more detail, use the following command:
Similarly, to examine a component device, type:
mdadm --detailcommand displays information about a RAID device,
mdadm --examineonly relays information about a RAID device as it relates to a given component device. This distinction is particularly important when working with a RAID device that itself is a component of another RAID device.
mdadm --querycommand, as well as both
mdadm --examinecommands allow you to specify multiple devices at once.
Example 6.1. Reviewing RAID configuration
Assume the system uses configuration from Figure 6.7, “Sample RAID Configuration”. You can verify that
/dev/md0is a RAID device by typing the following at a shell prompt:
mdadm --query /dev/md0/dev/md0: 125.38MiB raid1 2 devices, 0 spares. Use mdadm --detail for more detail. /dev/md0: No md super block found, not an md component.
As you can see, the above command produces only a brief overview of the RAID device and its configuration. To display more detailed information, use the following command instead:
mdadm --detail /dev/md0/dev/md0: Version : 0.90 Creation Time : Tue Jun 28 16:05:49 2011 Raid Level : raid1 Array Size : 128384 (125.40 MiB 131.47 MB) Used Dev Size : 128384 (125.40 MiB 131.47 MB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 0 Persistence : Superblock is persistent Update Time : Thu Jun 30 17:06:34 2011 State : clean Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 UUID : 49c5ac74:c2b79501:5c28cb9c:16a6dd9f Events : 0.6 Number Major Minor RaidDevice State 0 3 1 0 active sync /dev/hda1 1 3 65 1 active sync /dev/hdb1
Finally, to list all presently active RAID devices, type:
cat /proc/mdstatPersonalities : [raid0] [raid1] md0 : active raid1 hdb1 hda1 128384 blocks [2/2] [UU] md1 : active raid0 hdb2 hda2 1573888 blocks 256k chunks md2 : active raid0 hdb3 hda3 19132928 blocks 256k chunks unused devices: <none>