The Startsector of the Partition should NEVER be odd, rather even. 65536
would be fine, that's why lsblk gives an alignment of -1 for
scapa-backup I guess.
It does not matter if you use MBR or GPT, well, not too much for this
matter. The GPT is 34 LBA blocks (of 512 bytes). It can possibly be
longer to host more than 128 Partition entries, but no way close to 2048
which would resemble 1MByte. So 2048s would be a good place to start
your partition. It is aligned to 1 MByte, as well as 4KByte ... it even
is aligned to all major SSD Page-Sizes and SSD Erase-Block-Sizes.
Anyhow you either need to align the start of your partition or you'll
have an extremly hard time aligning the dm-crypt offset manually at the
right place.
Regards
-Sven
P.S.: If you still have a chance to change things, better do it now!
Am 04.01.2016 um 23:20 schrieb Yves-Alexis Perez:
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@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@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@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,
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