open_container__info_stream: ERROR: Couldn't read block 0 in order to determine block size.

[chriskuku]

drat 0.1.3:

I'm wondering why I'm suddenly getting this, although an fsck_apfs /dev/disk3s2 works. (reporting an error)?

$ sudo fsck_apfs /dev/disk3s2
** Checking the container superblock.
   Checking the checkpoint with transaction ID 263004.
** Checking the space manager.
** Checking the space manager free queue trees.
** Checking the object map.
** Checking volume.
** Checking the APFS volume superblock.
   The volume BackupNeu was formatted by diskmanagement (1677.141.3.7.2) and last modified by apfs_kext (1677.141.3.7.2).
** Checking the object map.
error: (oid 0x1c8eeb) om: btn: invalid o_type (0x40000002, expected 0x40000003)
   Object map is invalid.
** The volume /dev/disk3s2 could not be verified completely.
$ sudo ./drat inspect --container /dev/disk3s2
Opening `/dev/disk3s2` in read-only mode ... OK.
Determining block size ... read_block: ERROR: `fread()` encountered an unknown error whilst reading from the stream.
open_container__info_stream: ERROR: Couldn't read block 0 in order to determine block size.

[jivanpal]

You are likely giving Drat the device node of an APFS volume (which is not an actual block device), rather than that of the APFS container or underlying partition that the filesystem resides in. fsck_apfs works this out automatically, but Drat doesn't. See this comment and the ones preceding it for an explanation.

[chriskuku]

Thanks. I understand. Using

Opening `/dev/disk3` in read-only mode ... OK.
Determining block size ... 4096 bytes.
Simulating a mount of the container.
Reading block 0 ... validating ... OK.

Details of block 0:
--------------------------------------------------------------------------------
Stored checksum:    0x38d846a9f0105e81
OID:                0x1
XID:                0x4035c
...
...

Now it works. OK, fine. But how can drat help me to repair or fix the error, that fsck_apfs is reporting (in my original post)?

[jivanpal]

You should be able to use Drat's other subcommands to explore the filesystem. Try drat list /dev/disk3 0 / to explore the root of the first APFS volume. Once salvageable files are identified, they can be recovered using drat recover.

For general help, run drat or drat <subcommand>, e.g. drat list.