![]() ![]() Replacing a disk in the array with a spare one is as easy as: # mdadm -manage /dev/md0 -replace /dev/sdb1 -with /dev/sdd1 If the above command does not successfully add /dev/sdb1 back to the array, use the command from Example #1 to do it.Īlthough mdadm will initially detect the newly added device as a spare, it will start rebuilding the data and when it’s done doing so, it should recognize the device to be an active part of the RAID: Raid Rebuild Status Example 4: Replace a Raid device with a specific disk # mdadm -assemble /dev/md0 /dev/sdb1 /dev/sdc1 We choose option b), and will start by stopping the array to later reassemble it: # mdadm -stop /dev/md0 So we have 2 choices: a) add /dev/sdb1 as a spare, as shown in Example #1, or b) remove /dev/sdd1 from the array and then re-add /dev/sdb1. We will run into an error: mdadm: -re-add for /dev/sdb1 to /dev/md0 is not possibleīecause the array is already made up of the maximum possible number of drives. If we attempt to re-add /dev/sdb1 to /dev/md0 right now: # mdadm -manage /dev/md0 -re-add /dev/sdb1 Up to this point, we have a working RAID 1 array that consists of 2 active devices: /dev/sdc1 and /dev/sdd1. Example 3: Re-adding a device that was part of the array which had been removed previously Once the device has been indicated as failed manually, it can be safely removed from the array: # mdadm -manage /dev/md0 -remove /dev/sdb1 ![]() Not only that, but the recovery and rebuilding of raid data start immediately as well: Recover and Rebuild Raid Data Note how the spare device added in the previous example is used to automatically replace the failed disk. This is a mandatory step before logically removing the device from the array, and later physically pulling it out from the machine – in that order (if you miss one of these steps you may end up causing actual damage to the device): # mdadm -manage /dev/md0 -fail /dev/sdb1 You will typically add a new device when replacing a faulty one, or when you have a spare part that you want to have handy in case of a failure: # mdadm -manage /dev/md0 -add /dev/sdd1Īdd Device to Raid Array Example 2: Marking a RAID device as faulty and removing it from the array Example 1: Add a device to the RAID array The highlighted text in the previous image shows the basic syntax to manage RAIDs: # mdadm -manage RAID options devices Keep this fact in mind to avoid running into trouble further down the road. Note that if you omit the -manage option, mdadm assumes management mode anyway. Mark an array as ro (read-only) or rw (read-write).Replacing the faulty device with a spare one.Removing a faulty device from the array.To see what are the tasks that mdadm -manage will allow us to perform and how: Manage RAID with mdadm ToolĪs we can see in the above image, managing a RAID array involves performing the following tasks at one time or another: Thus, let’s start by typing: # mdadm -manage -help Understanding mdadm Options and Usageįortunately, mdadm provides a built-in -help flag that provides explanations and documentation for each of the main options. That said, feel free to go ahead and add this page to your browser’s bookmarks, and let’s get started. RAID Testing ScenarioĪs in the last article of this series, we will use for simplicity a RAID 1 (mirror) array which consists of two 8 GB disks ( /dev/sdb and /dev/sdc) and an initial spare device ( /dev/sdd) to illustrate, but the commands and concepts listed herein apply to other types of setups as well. In this tutorial we will review the functionality provided by this tool so that you can have it handy when you need it. ![]() Manage Raid Devices with Mdadm in Linux – Part 9 Regardless of your previous experience with RAID arrays, and whether you followed all of the tutorials in this RAID series or not, managing software RAIDs in Linux is not a very complicated task once you have become acquainted with mdadm -manage command. ![]()
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