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I've a drive that's part of a single disk RAID 1 array, it's a 2Tb Western Digital WD20EFRX-68EUZN0 (/dev/sdd). It's working fine, but I'm trying to set up another disk to join the array. The first disk is set up as follows;

gdisk -l /dev/sdd
GPT fdisk (gdisk) version 1.0.1

Caution! After loading partitions, the CRC doesn't check out!
Warning! Main partition table CRC mismatch! Loaded backup partition table
instead of main partition table!

Warning! One or more CRCs don't match. You should repair the disk!

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: damaged

****************************************************************************
Caution: Found protective or hybrid MBR and corrupt GPT. Using GPT, but disk
verification and recovery are STRONGLY recommended.
****************************************************************************
Disk /dev/sdd: 3907029168 sectors, 1.8 TiB
Logical sector size: 512 bytes
Disk identifier (GUID): D8BDF1E0-174F-4057-8206-3DB18C296D03
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 3907029134
Partitions will be aligned on 2048-sector boundaries
Total free space is 2157 sectors (1.1 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048      3907028991   1.8 TiB     FD00  primary

However, I'm not sure what to do about this now. My data is backed up, but I'm trying to work out how this error arose and how to fix it. I noticed this problem when trying to partition the second disk to match it. This is how I've got the second disk (/dev/sdc) set up;

gdisk -l /dev/sdc
GPT fdisk (gdisk) version 1.0.1

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.
Disk /dev/sdc: 3907029168 sectors, 1.8 TiB
Logical sector size: 512 bytes
Disk identifier (GUID): B3D36AE2-3C5F-4930-83F5-408756369412
Partition table holds up to 128 entries
First usable sector is 2048, last usable sector is 3907029134
Partitions will be aligned on 2048-sector boundaries
Total free space is 0 sectors (0 bytes)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048      3907029134   1.8 TiB     FD00  

However, the end sectors are different. Note I've not added the sdc drive to the array so I don't know how that changes things, not at all I suspect.The first disk is odd as both partitions have a start sector of 2048, but this first disk has a first useable sector at 34, and the second at 0.

Should I try to fix this, or just copy every file to the first disk, build my array off that, format the second disk to match and add that to the array?

Thanks!

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Ok, this was pretty silly in the end. I'd created a partition properly, but when making the array I'd used the whole disk(/dev/sdc) rather than the partition (/dev/sdc1) which meant that the gpt partition was damaged.

From what I'd read, it's better to use a slightly smaller partition rather than a whole disk, so if you get another HD from a different batch that doesn't have quite the same number of blocks as the original drive, you've given yourself a little more headroom. This is at the expense of a little bit of space.

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