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Partitioning, general information
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Summary:
some general information about partitioning schemes, the MBR
(master boot record) and how to recover/rebuild partition tables.
DiskPatch allows you to address problems that are caused by damage
to these structures.
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Keywords:
rebuild partition tables, MBR damage, Fdisk, deleted partition
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Created: 28-11-2006
Last edited: 20-01-2010
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| The Partition Table |
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Before you can store data on a hard disk it needs to be
partitioned. Consider a partition to be an area of the hard disk (or
even the entire disk) that is set aside for use by an operating
system such as Windows. All operating systems need to have at least
one partition to write data to; simply writing to an un-partitioned
(empty) disk is impossible. So even when you only have a 'c: drive' the disk is still
partitioned; at least one partition is required to be able to
write data to a disk using the operating system.
There are several advantages to dividing a hard disk into multiple partitions:
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Multiple partitions can help you organize your hard disk into several
sections. You could for example have one partition to install your
operating system in, one for your programs and one to store your
data.
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Dividing a hard disk into multiple partitions can also simplify the
process of creating backups and creating so called disk images with
for example Symantec's Ghost disk imaging software.
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Dividing the hard disk in multiple partitions also increases safety;
file system corruption will probably affect only one partition while
the data in other partitions remains intact.
The Master Boot Record (the first sector on the disk, also known as
the MBR) contains the information that describes the primary
partitions: the partition table. |
| The active
partition, visible and hidden partitions |
An active partition is the partition that the computer will try to
start the operating system from. Operating systems such as Windows,
OS/2, DOS and Linux are usually installed in an active partition.
There must be at least one active partition on the disk if that disk
should be used to start the computer.
If no active partition is set, or if multiple partitions are set
active, the system will fail to boot from the hard disk.
If you have a multiple boot configuration (multiple operating
systems installed on one hard disk; this usually means that there is
more than one partition, each containing an operating system) it may be
desirable to hide
primary partitions you are not currently booting from. |
| The MBR boot loader program |
Apart from the primary partition table, the MBR
also contains boot code that is required to start your computer. This
boot code is the first program code that is executed after the
system BIOS finishes its self tests (also known as POST,
Power On Self Test).
The main purpose of the boot program code is to locate the
active partition. |
| Backing up the MBR and
Partition Table(s) |
The MBR is a single point of failure! If
it is overwritten or becomes corrupted you will lose
access to all partitions and your data.
All primary partitions are defined in the MBR's partition
table. The extended partition, which is the starting point for
a chain of partition tables defining your logical partitions,
is also defined in the MBR. If this chain is broken at any
point you will lose access to one or more logical partitions.
The MBR and the partition tables are just a few sectors,
but they are vital sectors: if they become damaged you will
lose access to your data.
Having backups of these vulnerable areas will simplify
recovering data that was lost due to damage to the MBR, the
partition table(s) and boot sectors. |
| Partition Table Repair and
Recovery |
A damaged MBR or corrupted partition
table
will almost always result in mass data loss; access to entire partitions or even the entire hard disk is lost.
Even accidental partition deletion will make all data in the
deleted partition inaccessible. Recreating the partition with
Disk management or Fdisk will only increase the damage.
To recover the data in the lost partitions special data
recovery software is required that can find the lost
partitions and reconstruct the partition table(s) while leaving
the contents of the partitions intact. Reconstruction of
partition tables on the disk itself is referred to as
'in-place' repairs.
Whatever software you select for this task, it must be
able to undo the repairs in case the repairs lead to undesired
results! |
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