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How many maximum partitions can we create on a single drive? I remember getting error once when I had created somewhere around 16 partitions on same disk. Why put this limit? What is the problem with unlimited partitions?

I know that there can be four primary partitions for historical reasons and they get stored in first 512 bytes. So we use last partition info to point to another partition table. And after that we sort of create linked list of partitions. I just wanted to know why put a limit at all? There must be some benefit. Just because at that time no one created more than 16 partition, does not make sense putting a limit for 16 partition. There should be some gain to by putting a limit. Or some theoretical reason like we have for maximum supported file size on partition.

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7 Answers 7

Four primary/extended partitions. If you an extended partition you can have any number of logical disks within that extended partition. On a standard format disk the partition table only has room for four entries. If you upgrade the disk to GPT I think the limit changes, though I'm not sure what the new limit is.

JR

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For Master Partition Table disks the limit is based on the size of the partition table in the Master Boot Record (512 bytes IIRC), which was invented by IBM back in the 80's. Also, certain OSs have their own limits for a variety of reasons. The standard, such as it is, allows the Extended partition to have up to 24 partitions in it. Why the limit? Same as many limits, it seemed large enough to be 'good enough'. Also, in practice at the time the various OS kernels were under development partition counts rarely got that high.

This, by the way, is why many OSs implement their own version of partitioning. LVM gets around this on Linux. GPT is the Windows way of handling partitioning without an old fashioned Partition table. NetWare's NSS file-system runs a lot like LVM in that there is a single 'partition' that is then sub-divided in the media manager.

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The limit of 24 might be related to the practice of using single letters as drive letters. Minus A+B (usually assigned to floppies) gives you 24 letters to use. –  romandas Aug 6 '09 at 23:01
    
With 3 primary partitions, and 24 logical partitions in the one extended partition, it allows up to 27 total usable partitions per hard-disk. –  sysadmin1138 Aug 6 '09 at 23:13

The real question here, I think, is why you would want to create so many partitions in the first place. Storage space is not expensive, SATA is now standard, and there are, IMO, many better alternatives to partitioning a drive 33-odd times.

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A buddy was experimenting with some weird extents-based MD+LVM on Linux, and Linux apparently has a hard 63 partition limit on any disk. I'm not sure if that's filesystems per extended partition, or what. I'd like to think that in today's day and age, it's relatively irrelevant.

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I got error after 16 partitions using Linux. I use Fedora distributions generally. Is the limit different from one Linux distribution to another? –  Saurabh Barjatiya Jul 9 '09 at 17:30
    
16 normal partitions (when using extended partitions) the imit under lvm is 255 logical volumes –  Jure1873 Jul 9 '09 at 20:08

Although limits are determined by limitations such as space (the refered to 512 bytes), it is not uncommon for some limits to be set only because "if you are hitting this limit then you are doing something wrong".

In the "old days", why would you need to split your 40 MB hard drive (as I had) into more than one partition? Maybe a few users had that need, but most like myself would have been doing it "the wrong way" if instead of directories we wanted to create partitions.

As mentioned, LVM is one way around the limitation. ZFS is another, however instead of thinking of partitions, you throw drives into a zpool and create as many "filesystems" as you would like. In some demos I've seen thousands of ZFS filesystems so even thou it's not the same as partitioning the drive into thousands of segments you get all the benifits of segmentation with almost none of the disadvantages.

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While the extended/logical partition scheme theoretically provides an unlimited number of logical partitions, all operating systems sets some limit (as far as I know).

For DOS/windows, it cannot support more than a maximum of 24 partitions because it runs out of drive letters (C: to Z:) (plus any partitions with unsupported filesystem).

For Linux the maximum is limited by the allocation of minor device numbers. For traditional IDE disks there is support for 63 partitions, while SCSI disks are limited to 15 partitions.

For OpenBSD, FreeBSD, MachOS and others I do not know, but I am quite sure they have some limit.

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No, Windows is not limited to only drive letters. You can mount partitions to any NTFS folder. I'm not familliar with any limits thereafter.

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The original question doesn't seem to be just 'Windows-only'. –  romandas Aug 6 '09 at 23:04

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