[dm-crypt] Alignment issue with 4K disk

Yves-Alexis Perez corsac at debian.org
Mon Jan 4 23:20:46 CET 2016


On lun., 2016-01-04 at 22:54 +0100, Sven Eschenberg wrote:
> Hi,
> 
> start=4194304 -> assumind this is in 512 byte blocks, the start sector 
> is aligned to MByte boundary and thus 4k boundary.
> 
> Anyway, if your device only has one partition which is encrypted with 
> dm-crypt, set it up to start at sector 2048 (which should be default for 
> parted, fdisk and so on). Pass align-payload 2048 during creation of the 
> LUKS header, which will give you an MByte boundary and should always be 
> okay.
> 
> If the kernel still complains, then something else might be going wrong.

Right now I have:

root at scapa:~# lsblk -o +ALIGNMENT /dev/sdc
NAME             MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT        ALIGNMENT
sdc                8:32   0 931.5G  0 disk                            0
└─sdc1             8:33   0 931.5G  0 part                          512
  └─scapa-backup 253:4    0 931.4G  0 crypt /mnt/scapa-backup        -1

And:

scapa-backup: 0 1953336209 crypt aes-xts-plain64
0000000000000000000000000000000000000000000000000000000000000000 0 8:33 65536

root at scapa:~# fdisk -l /dev/sdc
Disk /dev/sdc: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 33553920 bytes
Disklabel type: gpt
Disk identifier: EBA98857-89BA-4B2C-8366-4A77A527A8E0

Device     Start        End    Sectors   Size Type
/dev/sdc1  65535 1953467279 1953401745 931.5G Linux filesystem

Partition 1 does not start on physical sector boundary.

[I'm a bit concerned with that, but since I'm using a GPT and not MBR it might
be related]

root at scapa:~# 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: 1953525168 sectors, 931.5 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): EBA98857-89BA-4B2C-8366-4A77A527A8E0
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 1953525134
Partitions will be aligned on 8-sector boundaries
Total free space is 123356 sectors (60.2 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1           65535      1953467279   931.5 GiB   8300  scapa-backup

Regards,
-- 
Yves-Alexis

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