Date: Wed, 27 Feb 2002 12:11:19 -0800 (PST) From: Kelly Yancey <kbyanc@posi.net> To: gemorga2 <gemorga2@vt.edu> Cc: scsi@FreeBSD.ORG Subject: RE: IDE vs. SCSI partition and slice limits Message-ID: <20020227120524.W8086-100000@gateway.posi.net> In-Reply-To: <3C7D3F5E@zathras>
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On Wed, 27 Feb 2002, gemorga2 wrote:
> So is that 30 slices inside a PC style partition or thirty partitions (as DOS
> considers "primary" partitions). I heard (probably incorrectly) that a "DOS"
> readable partition table has only 4 "slots" for "primary" partitions. With
> extended partitions I know you can have lots of "logical drives".
>
The Master Boot Record only has room for 4 partitions (FreeBSD "slices").
However, one of these partitions can be marked as an extended partition which
begins with another MBR, again with 4 partitions. In theory one can create a
tree structure describing partitions this way, however in practive it must be
a list (degenerate tree). Nonetheless, as Bruce pointed out, one can have
large numbers of partitions (limited only be disk space), but only a maximum
of 4 of them can be described by the MBR itself. Any tool that only knows how
to work with the MBR is limited to manipulating those 4 records. FreeBSD
itself, can deal with additional partitions as defined in the extended
partitions' MBR records also. Again, "partition" = "slice" in FreeBSD
parlance.
Kelly
kbyanc@{posi.net,FreeBSD.org}
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