Partition Tables

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DevynCJohnson

Guest
Many computer users are familiar with the basic idea of filesystems. A storage device is divided into partitions each formatted to a particular filesystem that holds files. Well, just as the filesystem hold the files, a partition table holds the filesystems. There are a few partition table types. The most commonly known one is MBR.

Master Boot Record (MBR) - Most IBM-based PC storage units use this partition table format. MBR is often referred to as the msdos partition table. The MBR can only support storage devices up to two terabytes. MBR supports the concept of logical and primary partitions. A storage unit with the MBR table can only have up to four primary partitions. Many users wanting to make a multiboot system with more than four Linux distros often have the problem of not being able to support more partitions. Remember, logical partitions cannot be made bootable. Multiboot systems must use a different partition table discussed later.

GUID Partition Table (GPT) - Some IBM-based PC storage units have GPT, although it is usually because the user reformatted from MBR to GPT. However, most Intel-based Mac systems use GPT by default. The GPT partition table offers many improvements over MBR. GPT can support storage units up to over nine zettabytes. GPT is also the most highly recommended partition table for computers needing more than four operating systems on one hard-drive. For example, if a computer with a ten terabyte hard-disk is meant to be a multiboot system for seven different Linux distros, then GPT should be used. Most Unix and Unix-like operating systems can fully support GPT. However, most Windows systems cannot run on a GPT partition table. As for Mac systems, only the Intel-based ones can boot from GPT.

Apple Partition Map (APM) - The PowerPC-based Mac systems can only boot from APM partition tables. This is usually referred to as the Mac or Apple partition table. Linux and Intel-based Macs can use APM. Windows does not support APM.

Amiga rigid disk block (RDB) - Amiga systems use the RDB partition table. These partition tables support up to about 4*10^19TB. That is forty quintillion terabytes.

AIX – The AIX partition table is used by proprietary AIX systems. By default, Linux does not natively support the AIX partition table.

BSD – BSD Unix systems can use the BSD partition table. Linux and Windows cannot read BSD partition tables.

Others - Some other partition table formats are listed below. The below listed are very rarely used. Not much information can be seen on the Internet about them.

dvh
humax
pc98
sgi
sun



Removable Storage - You may be wondering, "Which partition table do flash drives, SD cards, etc. use?". Well, since all systems can at least read MBR, the majority of mobile/removable storage uses MBR.

Formatting the partition table - To change or reformat a partition table, use Gparted and click "Device > Create Partition Table". Then, choose the desired partition table. Alternately, Parted can be used to format a storage device with a particular partitioning table (also called a "disk-label"). Doing so will erase all partitions and data on the selected storage device. The command is "parted mklabel DISKLABEL". The command requires Root privileges. The user will need to create new partitions for the storage device. Supported partitioning tables (supported by parted) include the listed below.
  • bsd
  • loop (raw disk access)
  • gpt
  • mac (Apple Partition Map (APM))
  • msdos (commonly called MBR)
  • pc98
  • sun

WARNING: Changing the partition table will erase the filesystems, partitions, and files. This is a more “low-level” format. However, the files are not truly gone. Read http://www.linux.org/threads/undelete-files-on-linux-systems.4316/ to fully understand the “deletion” of files.

You may also be wondering which is the best one for you. Well, use MBR with Windows and mobile systems (like Android), APM on PowerPC Macs and iOS, RDB on Amiga, and GPT on all other systems. However, you may have specific reasons for placing an OS on a different partition table than what is recommended one sentence previous.
 

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alug_Doc

Guest
You might want to add one more partition to your repertoire:

Creating an EFI partition

If you are manually partitioning your disk in the Ubuntu installer, you need to make sure you have an EFI partition set up.

1. If your disk already contains an EFI partition (eg if your computer had Windows8 preinstalled), it can be used for Ubuntu too. Do not format it. It is strongly recommended to have only 1 EFI partition per disk.

2. An EFI partition can be created via a recent version of GParted (the Gparted version included in the 12.04 disk is OK), and must have the following attributes:

1. Mount point: /boot/efi (remark: no need to set this mount point when using the manual partitioning, the Ubuntu installer will detect it automatically)

2. Size: minimum 100Mib. 200MiB recommended.

3. Type: FAT32

4. Other: needs a "boot" flag.
From: UEFI

I understand that this partition may be necessary on some systems and should be located before swap, root, and home.
 
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DevynCJohnson

Guest
I ran into a major problem installing Linux on a flash drive and was hoping someone could give me some assistance:

First of all, I am a newbie using a Linux Cert Guide for study purposes and went through a project for installing Fedora 13 (I need to use 13 since it is for an upcoming class). I installed the Basic Installation with GNOME on a flash drive and it was just fine (ext4 filesystem as well).

I tried a second installation on a 64gb flash using ext3 filesystem, Basic Install and added almost all optional components (except Virtualization). The drive did not boot properly and now it cannot be formatted. It reports "media not available" when I view its properties.

I have also tried installing the Basic Install on a 32gb SD card and it also did not install properly, and the SD card now reports that it has a RAW format with a 31MB capacity (rather than 32GB). Here are some utilities I have tried:

- Disk Management from Windows 7...sees it as a 31MB drive; cannot format it
- diskpart from the command line. Did not work
- MiniTool Partition Wizard..did not allow me to fix the MBR
- EaseUS Partition Master...may work but $45 to register and did not see the flash drive when Windows 7 did
- GParted...also unable to format

I believe I will need a program to rebuild the MBR for both the 32GB and 64GB drives but I have been unsuccessful. I also tried BootIce, utilities in Ubuntu and Fedora but with no luck. I would like the SD card to see its full 32GB capacity and allow me to format it, as with the 64GB flash drive.

If anyone has some suggestions or have had similar experiences and found a solution, I would be greatful. Being a newbie, I'm not nearly as seasoned with the command line as I am with DOS so any help would be appreciated.

Thank you all.
You can get more help by posting your question in the forums as its own thread.
 
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Cupán Tae

Guest
Nice round-up there, thanks!

One correction: Linux can boot from logical partitions! Windows, Haiku, BSD, Plan 9, Minix all can not however.

And one extra (possibly) interesting point is that BSD slices are *within* partitions.
 
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DevynCJohnson

Guest
@Cupán Tae , yes I find BSD slices interesting. However, as for Linux and logical partitions, I have heard people say that Linux can boot from logical partitions and some people say the opposite. I have tried to test it myself, but without success. That is why I recommend using GPT with Linux rather than MBR so that the whole "logical partition" concept can be avoided.
 

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