[conspire] Comments on setting up disk partitions.

Rick Moen rick at linuxmafia.com
Thu Apr 9 11:40:02 PDT 2009

Quoting jim (jim at well.com):

> QUESTION: are there technial restrictions to choosing the first
> primary partition to be the extended partition? 


I'm pretty sure that /sbin/fdisk will let you declare any or all of the
four physical entries in an IBM/Microsoft partition table to be of type
"extended" -- in accordance with the Unix philosophy of giving you
enough rope to hang yourself plus a few yards more, just to make sure.

However, prudence suggests having only _one_ extended partition, and
having it be after any primary partitions that exist, in order to
minimise the likelihood of freaking out other software that doesn't
expect weird partition schemes.

> QUESTION: after a little looking, i'm not clear as to the upper
> limit of possible partitions on a linux system. for now i'm assuming
> fifteen usable partitions, three primary, one extended, and twelve
> logical (where the extended partition is not usable in the sense of
> impressing a filesystem on it and storing data). 

The limiting factor is one of allocated Linux device numbers.  If using
the /dev/hdXX scheme of the legacy "drivers/ide" driver set, then you
get 31 filesystems (supportable) per physical disk, because that's how
many "minor device" numbers are availble under major number 3.  If using
the more modern /dev/sdXX scheme such as is used by Jeff Garzik's
"libata" driver set (that leverages the SCSI layer; thus the "s"), then
you get 15 filesystems (supportable) per physical disk, because that's
how many "minor device" numbers are available under major number 8.

See:  http://www.lanana.org/docs/device-list/devices.txt

> QUESTION: i'm not clear on the preferred spelling of "filesystem"
> or "file system". 

This is English.  We have no Academie Anglais.  ;->

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