[parted-devel] Diagnosing a "loop" partition

[David Liontooth]

On an Areca controller, in JBOD mode, I used cfdisk to create a single 
partition, and mksf.xfs for the file system.

On reboot, Linux 2.6.27.9 reports "unknown partition table", while 
parted identifies the partition table type as "loop":

# parted /dev/sdac
GNU Parted 1.8.8        
Using /dev/sdac
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) print                                                           
Model: Seagate ST31000340NS (scsi)
Disk /dev/sdac: 1000GB
Sector size (logical/physical): 512B/512B
Partition Table: loop

Number  Start  End     Size    File system  Flags
 1      0.00B  1000GB  1000GB  xfs              

(parted) print 1                                                         
No Implementation: Support for opening xfs file systems is not 
implemented yet.

An octal dump shows:

# od -tx1 -Ax -N512 /dev/sdad
000000 58 46 53 42 00 00 10 00 00 00 00 00 0e 8e 0d b6
000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
000020 06 a8 a8 db 91 f3 45 4a 84 80 87 11 62 35 93 3b
000030 00 00 00 00 08 00 00 04 00 00 00 00 00 00 00 80
000040 00 00 00 00 00 00 00 81 00 00 00 00 00 00 00 82
000050 00 00 00 01 03 a3 83 6e 00 00 00 04 00 00 00 00
000060 00 00 80 00 b4 a4 02 00 01 00 00 10 32 30 30 38
000070 5f 30 33 73 00 00 00 00 0c 09 08 04 1a 00 00 19
000080 00 00 00 00 00 00 00 40 00 00 00 00 00 00 00 3d
000090 00 00 00 00 0e 8d 8d a2 00 00 00 00 00 00 00 00
0000a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0000b0 00 00 00 00 00 00 00 02 00 00 00 00 00 00 00 00
0000c0 00 00 00 00 00 00 00 01 00 00 00 08 00 00 00 08
0000d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
*
000200

In contrast, a working drive shows:

# parted /dev/sdaa
GNU Parted 1.8.8
Using /dev/sdaa
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) print                                                           
Model: Seagate ST31000340NS (scsi)
Disk /dev/sdaa: 1000GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    Type     File system  Flags
 1      32.3kB  1000GB  1000GB  primary  xfs              

(parted)  print 1                                                         
No Implementation: Support for opening xfs file systems is not 
implemented yet.

The octal dump for the working drive:

# od -tx1 -Ax -N512 /dev/sdaa
000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
*
0001b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01
0001c0 01 00 83 fe ff ff 3f 00 00 00 82 59 70 74 00 00
0001d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
*
0001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 aa
000200

The drives with unknown partition tables are backups, and losing them 
would not be a disaster, but parted plausibly reports a full file system 
-- I have no reason to believe it's damaged.

Is there any way to modify the claimed "loop" partition so that the OS 
can see it?

Is this really a loop partition, and if so, what's its proper usage?

Is xfs support planned for parted?

Dave