mjhjmtu

I have a disk that was in a mdadm raid1 with a btrfs partition.
Now I want to use this partition without the raid stuff and mount it normally.
I already zeroed the mdadm superblock, but now the offsets that mdadm created are still present and I can't mount the partition.
Before I deleted the superblock, I noted that the data offset was 2048.

What can I do now? I would try to move the partition by that 2048 bit, but I'm not sure how to do that exactly.

Wouldn't it be enough to alter the parition table and set the begin sector 2048 bits further?

Edit:
Here is the full information from mdadm

mdadm --examine /dev/sdb
/dev/sdb:
 MBR Magic : aa55
Partition[0] : 4980480 sectors at 2048 (type fd)
Partition[1] : 4194304 sectors at 4982528 (type fd)
Partition[2] : 11329536 sectors at 9437184 (type fd)
root@debian-test:/home/debian# mdadm --examine /dev/sdb3
/dev/sdb3:
 Magic : a92b4efc
 Version : 1.2
 Feature Map : 0x0
 Array UUID : 8bd40f46:896acdc5:6f3fa1f7:67f779fc
 Name : dsm-virtualbox:2
 Creation Time : Thu Jul 12 23:05:16 2018
 Raid Level : raid1
 Raid Devices : 1

 Avail Dev Size : 11327488 (5.40 GiB 5.80 GB)
 Array Size : 5663744 (5.40 GiB 5.80 GB)
 Data Offset : 2048 sectors
 Super Offset : 8 sectors
 Unused Space : before=1968 sectors, after=0 sectors
 State : clean
 Device UUID : 5cf0a635:f107d2b7:18498037:0a9d68f7

 Update Time : Thu Jul 12 23:29:40 2018
 Checksum : b3b49d3d - correct
 Events : 6


 Device Role : Active device 0
 Array State : A ('A' == active, '.' == missing, 'R' == replacing)

I'm only interested in partition 3, the rest are system paritions that I'll delete.

I am no expert for mdadm, but assuming raw data with just an offset, you are right since you can alter the partition table for accessing the partition as such. You probably need to delete the partition and then create a new partition at the desired location. The MBR is self contained, no data will be written to the partition itself (this is only true for primary partitions).

Alternatively, you can wrap a block device with a loop device, starting at a given offset. The offset reportedly is 2048 sectors, an equivalent of 2048 · 512 = 1048576 bytes.

offset=1048576
losetup -f /dev/sdb3 -o $offset

Then mount the newly created loop block device (usually /dev/loop0).

Or using mount directly:

mount -o loop,ro,offset=$offset /dev/sdb3 /mountpoint

(ro added for safety reasons during experiments.)