Partition TableMaster Boot Record: LogicalExtended


Partition Table/Master Boot Record: Logical/Extended

Continuing with the CHS model, we can achieve more than four partitions by utilizing extended partitions within a primary partition. Extended partitions are also known as logical partitions, and they can only exist within a primary partition with an extended flag, also known as a partition type (05) set.

In the following example, partition 1 is defined as "extended," as depicted by the fact that byte 1C2's value is equal to "05." We then define partition 1 to occupy 39690 sectors and contain two logical partitions.

[root@localhost root]# cfdisk -P rst /dev/hde Disk Drive: /dev/hde Sector 0: 0x000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ~~~~~ 0x190: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x1A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x1B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 0x1C0: 01 00 05 0E 3F 29 3F 00 00 00 CB 9A 00 00 00 00 0x1D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x1E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x1F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 AA Sector 63: 0x000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ~~~~~~ 0x1A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x1B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 80 02 0x1C0: 01 00 83 0E 3F 14 3F 00 00 00 07 4D 00 00 00 00 0x1D0: 01 15 05 0E 3F 29 46 4D 00 00 85 4D 00 00 00 00 0x1E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x1F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 AA Sector 19845: 0x000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ~~~~~~ 0x1A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x1B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 0x1C0: 01 15 83 0E 3F 29 3F 00 00 00 46 4D 00 00 00 00 0x1D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x1E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x1F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 AA Partition Table for /dev/hde             First    Last  # Type     Sector   Sector   Offset  Length   Filesystem Type (ID) Flags -- ------- -------- --------- ------ --------- ---------------- ---------  1 Primary     0    39689      63    39690  Extended (05)        None (00)  2  0x00       0    0    0 0x00    0    0    0        0          0  3  0x00       0    0    0 0x00    0    0    0        0          0  4  0x00       0    0    0 0x00    0    0    0        0          0  5 Logical       63*   19844      63    19782* Linux (83)        Boot (80)  6 Logical    19845    39689      63    19845  Linux (83)        None (00)    Pri/Log    39690 12594959       0 12555270  Free Space        None (00) Partition Table for /dev/hde          ---Starting---      ----Ending----    Start Number of  # Flags Head Sect Cyl   ID  Head Sect Cyl    Sector  Sectors -- ----- ---- ---- ---- ---- ---- ---- ---- -------- ---------  1  0x00    1    1    0 0x05   14   63   41       63     39627  5  0x80    2    1    0 0x83   14   63   20       63     19719  6  0x00    1    1   21 0x83   14   63   41       63     19782


A few items about logical partitions need to be noted. Notice how primary partitions are represented with numeric values 1, 2, 3, and 4, whereas logical partitions are represented with numeric values 5 and greater. In addition, notice the location of the bootable partition. We set the logical partition number to 5 for the boot device. When using LILO, this boot configuration will fail with old versions of LILO due to the 1024 sector limit. This limitation on LILO has been removed and never existed on GRUB.

Scenario 6-2: Multiple Partitions Exist, but fdisk Only Reports a Single Partition

As previously discussed, primary and extended partitions can be displayed through cfdisk, fdisk -l, or another tool. However, with Linux on IA64, fdisk reports only a primary partition. In the following example, we depict multiple partitions with extensible firmware interface (EFI), and fdisk reports only a single partition.

[root@atlorca2 root]# df Filesystem           1K-blocks      Used Available Use% Mounted on /dev/sda2             32891620   6077808  25143012  20% / /dev/sda1               102182      4598     97584   5% /boot/efi none                   2067344         0   2067344   0% /dev/shm [root@atlorca2 root]# fdisk -l /dev/sda Disk /dev/sda: 36.4 GB, 36420075520 bytes 255 heads, 63 sectors/track, 4427 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes    Device Boot    Start       End     Blocks   Id  System /dev/sda1             1      4428   35566479+  ee  EFI GPT


fdisk reports only a single partition because the Global Unique Identification (GUID) Partition Table (or GPT) is used with the extensible firmware interface (EFI) on IA64. Before we go into detail about the solution, let's discuss EFI for a moment.

EFI is nothing more than a firmware interface for the system's firmware (BIOS) that has the capability to call an OS's bootloader. A complete history can be found at http://developer.intel.com/technology/efi/efi.htm. Now let's proceed to the solution.

Solution 6-2

You can use other tools to review the partition table, such as partx,

partx /dev/sda # 1:        34-   204833 (   204800 sectors,   104 MB) # 2:    204834- 67036926 ( 66832093 sectors, 34218 MB) # 3:  67036927- 71132926 ( 4096000  sectors,  2097 MB)


or parted, as shown in the following example:

parted GNU Parted 1.6.3 Copyright (C) 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc. This program is free software, covered by the GNU General Public License. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. Using /dev/sda (parted) p Disk geometry for /dev/sda: 0.000-34732.890 megabytes Disk label type: gpt Minor    Start       End     Filesystem  Name                  Flags 1          0.017    100.016  fat16                             boot 2        100.017  32732.874  ext3 3      32732.875  34732.874  linux-swap (parted) ?   check MINOR                do a simple check on the filesystem   cp [FROM-DEVICE] FROM-MINOR TO-MINOR    copy filesystem to another \                                           partition   help [COMMAND]                prints general help, or help on COMMAND   mklabel LABEL-TYPE            create a new disklabel (partition table)   mkfs MINOR FS-TYPE            make a filesystem FS-TYPE on partition MINOR   mkpart PART-TYPE [FS-TYPE] START END      make a partition   mkpartfs PART-TYPE FS-TYPE START END      make a partition with a \                                             filesystem   move MINOR START END          move partition MINOR   name MINOR NAME               name partition MINOR NAME   print [MINOR]                 display the partition table, or a \                                 partition   quit                          exit program   rescue START END              rescue a lost partition near START and \                                 END   resize MINOR START END        resize filesystem on partition MINOR   rm MINOR                      delete partition MINOR   select DEVICE                 choose the device to edit   set MINOR FLAG STATE          change a flag on partition MINOR




Linux Troubleshooting for System Administrators and Power Users
Real World Mac Maintenance and Backups
ISBN: 131855158
EAN: 2147483647
Year: 2004
Pages: 129
Authors: Joe Kissell

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