It is a very strange problem. My usb harddisk has four partitions, one is primary, the other three are logical (contained within an extended partition). When I plug in the disk, three of the partitions are mounted automatically except one--the first logical partition in the extended partition.

Initially I thought it is the problem of system (at that time I used Mint). But after I change to Ubuntu 12.04, the problem wasn't solved. I don't want to add a rule in fstab, and I want to know what happened. The disk is fine, and the partition can be accessed in Windows and mounted manually.

result of dmesg | tail:

[100933.557649] usb 2-1.2: new high-speed USB device number 4 using ehci_hcd
[100933.651891] scsi8 : usb-storage 2-1.2:1.0
[100934.649047] scsi 8:0:0:0: Direct-Access     SAMSUNG                        PQ: 0 ANSI: 0
[100934.650963] sd 8:0:0:0: Attached scsi generic sg2 type 0
[100934.651342] sd 8:0:0:0: [sdb] 625142448 512-byte logical blocks: (320 GB/298 GiB)
[100934.651977] sd 8:0:0:0: [sdb] Write Protect is off
[100934.651989] sd 8:0:0:0: [sdb] Mode Sense: 03 00 00 00
[100934.652836] sd 8:0:0:0: [sdb] No Caching mode page present
[100934.652848] sd 8:0:0:0: [sdb] Assuming drive cache: write through
[100934.655354] sd 8:0:0:0: [sdb] No Caching mode page present
[100934.655367] sd 8:0:0:0: [sdb] Assuming drive cache: write through
[100934.734652]  sdb: sdb1 sdb3 < sdb5 sdb6 sdb7 >
[100934.737706] sd 8:0:0:0: [sdb] No Caching mode page present
[100934.737725] sd 8:0:0:0: [sdb] Assuming drive cache: write through
[100934.737731] sd 8:0:0:0: [sdb] Attached SCSI disk

result of parted -l:

Model: SAMSUNG  (scsi)
Disk /dev/sdb: 320GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    Type      File system  Flags
 1      32.3kB  21.5GB  21.5GB  primary   ntfs
 3      21.5GB  320GB   299GB   extended               lba
 5      21.5GB  129GB   107GB   logical   ntfs
 6      129GB   236GB   107GB   logical   ntfs
 7      236GB   320GB   83.8GB  logical   ntfs