09-21-2012
Quote:
Originally Posted by
fpmurphy
MBR partitions can be greater than 2Gb. GPT is required when your disk is greater than approx 2Tb and using 512 sector sizes.
Of course, it was a typo: I meant 2TB.
In MBR every partition is defined by its starting sector and its size in sectors. Both values are limited to 32 bits. So a partition max size, as well as its farthest possible starting point, is:
(2^32-1) x 512 = 2,199,023,255,040 bytes.
This means that you can use a MBR for two 1.5TB partitions in a 3TB disk, for instance. On the same disk you can't use MBR for a single 3TB partition, nor for four 750GB partitions, nor for two partitions of 0.5TB and 2.5TB ...
Today even disks having 4kB sectors show to the system virtual sectors of 512B. So the disk sector real size doesn't affect the 2TB limit.
--
Bye
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LEARN ABOUT NETBSD
diskpart
DISKPART(8) BSD System Manager's Manual DISKPART(8)
NAME
diskpart -- calculate default disk partition sizes
SYNOPSIS
diskpart [-d] [-p] [-s size] disk-type
DESCRIPTION
diskpart is used to calculate the disk partition sizes based on the default rules used at Berkeley.
Available options and operands:
-d An entry suitable for inclusion in the disk description file /etc/disktab is generated; for example, disktab(5).
-p Tables suitable for inclusion in a device driver are produced.
-s size The size of the disk may be limited to size with the -s option.
On disks that use bad144(8) type of bad-sector forwarding, space is normally left in the last partition on the disk for a bad sector forward-
ing table, although this space is not reflected in the tables produced. The space reserved is one track for the replicated copies of the ta-
ble and sufficient tracks to hold a pool of 126 sectors to which bad sectors are mapped. For more information, see bad144(8). The -s option
is intended for other controllers which reserve some space at the end of the disk for bad-sector replacements or other control areas, even if
not a multiple of cylinders.
The disk partition sizes are based on the total amount of space on the disk as given in the table below (all values are supplied in units of
sectors). The 'c' partition is, by convention, used to access the entire physical disk. The device driver tables include the space reserved
for the bad sector forwarding table in the 'c' partition; those used in the disktab and default formats exclude reserved tracks. In normal
operation, either the 'g' partition is used, or the 'd', 'e', and 'f' partitions are used. The 'g' and 'f' partitions are variable-sized,
occupying whatever space remains after allocation of the fixed sized partitions. If the disk is smaller than 20 Megabytes, then diskpart
aborts with the message ``disk too small, calculate by hand''.
Partition 20-60 MB 61-205 MB 206-355 MB 356+ MB
a 15884 15884 15884 15884
b 10032 33440 33440 66880
d 15884 15884 15884 15884
e unused 55936 55936 307200
h unused unused 291346 291346
If an unknown disk type is specified, diskpart will prompt for the required disk geometry information.
SEE ALSO
disktab(5), bad144(8)
HISTORY
The diskpart command appeared in 4.2BSD.
BUGS
Most default partition sizes are based on historical artifacts (like the RP06), and may result in unsatisfactory layouts.
When using the -d flag, alternative disk names are not included in the output.
BSD
June 6, 1993 BSD