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Hard disk
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drive (
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HDD) technology
Block device partitioning has a long history, related to the physical construction of hard disk drives – to their cylinders, heads and sectors. Current hard disk drives present themselves to the operating system as a simple sequence of blocks. For practical partitioning purposes the physical construction no longer matters except that Zone Bit Recording means that a partition at the beginning of the drive (physically the outer edge) transfers data faster than one at the end of the drive. With the introduction of 4k sector sizes, aligning partitions on sector boundaries has become important.
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Wikipedia advanced format (> 512 B sectors)
Solid state drive (SSD) technology
TBC
Partition tables
Reference: http://en.wikipedia.org/wiki/Partition_table
SSD partitioning considerations
SSDs need some free space for over-provisioning, so it's advised to leave about 5% unpartitioned (e.g. 8 GB from a 128 GB) - however, many new SSDs have this space reserved on firmware level so there's no need to do that. Usually that's the case if capacity is just a little lower than the closest power of 2: e.g. 120 instead of 128 GB, 60 instead of 64 GB, etc.
DOS partition table (a.k.a MBR)
Also known as the MBR partition table.
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Reference: http://en.wikipedia.org/wiki/Master_boot_record
The EBR/EPBR
Each logical partition is preceded by an Extended Boot Record (EBR) a.k.a. Extended Partition Boot Record (EPBR) of one sector followed by a number of unused sectors. There are commonly 62 unused sectors which, with the EBR, fill a historical 63 sector track.
Which partition management utility to use?
If grub is installed in the MBR, using gdisk or cgdisk will make the system unbootable by overwriting the MBR.
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There are several *fdisk programs around. Each has its problems and strengths. Try them in the order cfdisk, fdisk, sfdisk. (Indeed, cfdisk is a beautiful program that has strict requirements on the partition tables it accepts, and produces high quality partition tables. Use it if you can. fdisk is a buggy program that does fuzzy things - usually it happens to produce reasonable results. Its single advantage is that it has some support for BSD disk labels and other non-DOS partition tables. Avoid it if you can. sfdisk is for hackers only -- the user interface is terrible, but it is more correct than fdisk and more powerful than both fdisk and cfdisk. Moreover, it can be used noninteractively.)
These days there also is parted. The cfdisk interface is nicer, but parted does much more: it not only resizes partitions, but also the filesystems that live in them.
GUID partition table (GPT)
GPT is required when the HDD presents 512 kB sectors and is greater than 2 TiB and for UEFI boot.
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GRUB's GPT requirements
TODO: duplicated text!!! Merge this with similar information at UEFI and GPT and cross-reference as required.
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EFI systems: when GRUB is to be installed on a UEFI system, an "EFI System Partition (ESP)" is required (called "EFI boot partition" in Debian and Ubuntu documentation), partition type ef00. It has to be big enough to contain all the boot loaders that will be installed in it, say 100 MB for a single OS system and 200 MB for multi-boot.
Which partition management utility to use?
For GPT-partitioning, there is gdisk and its full-screen version cgdisk. They automatically do 4096 kB physical sector alignment.
Appendix – exact DOS partition sizes
Find an exact partition size
The easiest way to find an exact partition size is to read the /sys/block/sd*/sd*/size file, for example cat /sys/block/sda/sda2/size. This gives the size of the sda2 partition in sectors.
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sfdisk TBC
parted TBC
/proc/partitions The blocks listed are 1024 byte blocks, rounded down to the nearest integer.
Create a partition with an exact size
fdisk
The u option ("change display/entry units") toggles between cylinders and sectors. It changes the Start and End addresses but not the Blocks which are always shown as 1024 byte blocks. (Tested using util-linux 2.20.1).Note TODO: test the text below
When creating a new partition, the default starting block leaves 62 unused sectors after the EPBR. This results in a historically conventional 63 sector track before the partition itself.
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