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I have a RAID 10 array consisting of 4 disks. One of them has failed and I have removed it from the array.

I have purchased an identical new drive and am unsure about how to add the new drive to the array.

In some literature that I read, it was mentioned that I need to copy the partitions to the new drive. In other online material that I read it seemed like the drive was simply added to the array and the syncing began without any mention of partitions having to be copied.

So now I am unsure how to proceed.

Here is some info about my raid 10 array.

cat /proc/mdstat:

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md127 : active raid10 sda1[0] sdb1[1] sdc1[2] 5860267008 blocks super 1.2 512K chunks 2 near-copies [4/3] [UUU_]
unused devices: <none>

sudo mdadm --detail /dev/md127

mdadm: unreconised word on DEVICE line: UUID=8eac0a3d-a22c-1a92-6ed9-f147f3dea64f
mdadm: unreconised word on DEVICE line: UUID=246226d0-a621-7f34-87b6-ff33b5c55906
mdadm: unreconised word on DEVICE line: UUID=52e1afa6-3ca6-a96e-f3dc-99bd0f56e878
mdadm: unreconised word on DEVICE line: UUID=16843e03-f177-97ef-07a7-6d761de9e99b
/dev/md127: Version : 1.2 Creation Time : Sat Dec 13 15:01:15 2014 Raid Level : raid10 Array Size : 5860267008 (5588.79 GiB 6000.91 GB) Used Dev Size : 2930133504 (2794.39 GiB 3000.46 GB) Raid Devices : 4 Total Devices : 3 Persistence : Superblock is persistent Update Time : Mon Dec 31 22:07:21 2018 State : clean, degraded Active Devices : 3
Working Devices : 3 Failed Devices : 0 Spare Devices : 0 Layout : near=2 Chunk Size : 512K Name : server:0 (local to host server) UUID : 47c17420:8c4f5bf8:d70c8436:38187fe6 Events : 973 Number Major Minor RaidDevice State 0 8 1 0 active sync /dev/sda1 1 8 17 1 active sync /dev/sdb1 2 8 33 2 active sync /dev/sdc1 3 0 0 3 removed

gdisk -l of disk /dev/sda1 (in order to copy to new disk dev/sdd):

GPT fdisk (gdisk) version 0.8.8
Partition table scan: MBR: not present BSD: not present APM: not present GPT: not present
Creating new GPT entries.
Disk /dev/sda1: 5860530176 sectors, 2.7 TiB
Logical sector size: 512 bytes
Disk identifier (GUID): AF72F8BD-75D0-469A-A7D3-3A4A40EFFFBE
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 5860530142
Partitions will be aligned on 2048-sector boundaries
Total free space is 5860530109 sectors (2.7 TiB)
Number Start (sector) End (sector) Size Code Name

I would be very thankful for steps required to swap the failed drive.

1 Answer

This is a very straightforward and low-risk procedure: Assuming you have physically replace the drive, you need to

  • First of all, find the device name for the new disk: it should be something like /dev/sdX. To find it out, try cat /proc/partitions to identify the drive, that has exactly the same size as /dev/sda, /dev/sdb and /dev/sdc

  • Next we need to create the partition table. The easiest way is to run gdisk -l /dev/sda and note the exact values for /dev/sda1, then run gdisk /dev/sdX (with X the letter you identified before) and create an identical partition (if needed, you must apt-get install gdisk before)

  • Finally add the newly created partition to the array: mdadm --add /dev/md127 /dev/sdX1 (again with X as identified before)

When this is done, cat /proc/mdstat will show you the progress of the new disk being synchronized into the array.

3

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