Max usable disk space

[James Wilkinson]

Mark Haney wrote:
> Does anyone know the deal 
> with FDISK?  Are there plans to fix that little problem?  I mean pretty 
> soon 2TB is gonna be a drop in the bucket for most filesystems, and 
> considering ext3 handles 64TB or more, this seems a horrible limitation.

Dave Jones referred to it up-thread. For example:
http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/release-notes/as-zseries/RELEASE-NOTES-U1-s390x-en.html
says:
    · The commonly-used MS-DOS partition table format can not be used on
      devices larger than 2 TB. For devices larger than 2 TB, the GPT
      partition table format must be used. The parted utility must be
      used for the creation and management of GPT partitions. To create
      a GPT partition, use the parted command mklabel gpt.

Don't worry about the "zseries" or the "s390" in the URL: that's just
the system that's most likely to hit this issue. It's talking about the
same partition table format.

It's not a bug in fdisk: it does exactly what it's supposed to do --
handle MS-DOS style partition tables. It's those tables that can't
handle devices larger than 2 TB -- there just isn't enough space in the
fields. It's a harder limit than 640K was for real-mode DOS, or 2 GB was
for FAT16. Change the partition table format so it can handle larger
devices, and *it's not DOS partition table format any more*, and
operating systems that don't know about the new format can't use the
disk. At all.

And if you're going to go for something other than traditional MS-DOS
partitions, you might as well go for something with a reasonable -- er,
*any* design, that doesn't have the archaic "4 primary, one of which
may be extended, and umpteen logical" limitations. Like GPT.

Note that none of this refers to the format of filesystems within those
partitions (ext3, reiser, FAT32, etc). It refers to the way the
partitions themselves are defined and stored on disk. The partition
table chops up the disk into partitions, and then you put "normal"
filesystems in the partitions. [1]

James.

[1] Or not. Swap partitions and raw device access are beyond the scope
of this e-mail...



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