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Old 05-16-2013, 08:35 PM   #1
synchlavier
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Linux partitions and limitations


In recently reading an article on linux basics before I embark and my personal installation project I came across this passage -

http://www.ibm.com/developerworks/li...pic1-v3-102-1/

IDE drives have three types of partition: primary, logical, and extended. The partition table is located in the master boot record (MBR) of a disk. The MBR is the first sector on the disk, so the partition table is not a very large part of it. This limits the number of primary partitions on a disk to four. When more than four partitions are required, as is often the case, one of the primary partitions must instead become an extended partition. An extended partition is a container for one or more logical partitions. In this way, you can have more than 4 partitions on a drive using the MBR layout.


The MBR layout also limits the maximum size of disk that is supported to approximately two terabytes. The newer GUID Partition Table (or GPT) layout solves this size limitation and also the rather small limitation on the number of partitions. A disk formatted using GPT layout supports up to 128 primary partitions by default and does not use extended or logical partitions. For more information on MBR internals and how the GUID Partition Table (GPT) works, see MBR, EBR, GPT and LVM internals.


So when doing the math it would seem that only a total of 8 partitions 4 primary and the rest extended are allowed on a hdd - is that still the case today with modern SATA hdds -

Last edited by synchlavier; 05-16-2013 at 08:38 PM.
 
Old 05-16-2013, 08:57 PM   #2
TobiSGD
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On a disk that uses the MBR partition table (instead of the newer GPT partition tables) you can only have a maximum of 4 primary and extended partitions, not 4 primary and 4 extended partition. This is a limit of the MBR partition scheme and is independent of the underlying hardware, so as long as you MBR partitioning you will have that limitation with any disk.
 
Old 05-16-2013, 08:58 PM   #3
synchlavier
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TobiSGD - You stated you can only have a maximum of 4 primary and extended partitions, not 4 primary and 4 extended partition. So what you are saying then is that you can have a maximum of 8 partitions - one extended partition per primary partition ? Also allow me to ask do modern day laptops example HP, Acer and Toshiba use the newer GPT tables or do they still use the MBR ?

Last edited by synchlavier; 05-16-2013 at 09:04 PM.
 
Old 05-16-2013, 09:31 PM   #4
michaelk
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Nope, in a nutshell originally the max number of partitions on an IDE drive was 63. 4 primary including an extended and the rest were logical partitions. SCSI drives were limited to 15 partitions. When libata was developed it essentially made all drives i.e. USB, SCSI, SATA and IDE use the SCSI subsystem which then limited them to 15 partitions.

So with a MBR layout SATA drives have a 15 partition limitation.
 
Old 05-16-2013, 09:32 PM   #5
chrism01
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Actually, its badly phrased.

If you only have Primaries, then you can have a max of 4.
If you want more than 4 partitions, you'd go with 3 x Primary and 1 x Extended.
Note that an 'Extended' partition is not a 'real/normal', its a combination marker & container.
Basically, it contains a number of Logical partitions, which are 'real', whereas the Extended one is just an entry on the disk to tell the system where the Logicals start. You can't use it to put a file system in.
Have a read of https://en.wikipedia.org/wiki/Disk_p...mary_partition
 
Old 05-16-2013, 09:55 PM   #6
TobiSGD
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Quote:
Originally Posted by synchlavier View Post
TobiSGD - You stated you can only have a maximum of 4 primary and extended partitions, not 4 primary and 4 extended partition. So what you are saying then is that you can have a maximum of 8 partitions - one extended partition per primary partition ?
No, you can have a maximum number of 4 primary partitions. In that case you can't have an extended partition. Or you can have 3 primary partition and 1 extended partition (so that you still have a maximum of 4), where the extended partition can hold many logical partitions.
Quote:
Also allow me to ask do modern day laptops example HP, Acer and Toshiba use the newer GPT tables or do they still use the MBR ?
That depends how the manufacturer has configured the system. Many newer laptops that come with UEFI firmware and Windows 8 pre-installed use GPT partition tables, many Windows 7 laptops use th MBR tables. On new Linux versions it is up to you what you choose.
 
  


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