dangerously dedicated physical disks.

Warren Block wblock at wonkity.com
Sun Sep 22 14:25:31 UTC 2013

On Sun, 22 Sep 2013, atar wrote:

> During the reading of the FreeBSD handbook, I've encountered at the term 
> 'dangerously dedicated' regarding physical disks and the author of this 
> chapter in the FreeBSD handbook didn't think this term need more clarity. so 
> for newbies like me in the FreeBSD world I want to ask: what's the 
> 'dangerously dedicated' term meaning by?

The term refers to a disk partitioned with only the BSD disklabel 
partition table:

   disk ada0
     partition "a" (ada0a, /)
     partition "b" (ada0b, swap)
     partition "d" (ada0d, /var)
     partition "e" (ada0e, /tmp)
     partition "f" (ada0f, /usr)

It's "dangerous" because that partitioning format is rare outside of 
BSD-based systems.  Disk utilities may not recognize it, and could
damage it.

Most of the rest of the world used MBR partitioning, which allowed up to 
four MBR partitions (called "slices" by FreeBSD) per disk.

Since four slices is not enough for the standard FreeBSD disk layout, 
with /, swap, /var, /tmp, and /usr, the standard procedure is to use MBR 
partitioning, with the MBR partitions ("slices") being sub-partitioned 
by a BSD disklabel.

   disk ada0
     MBR slice 1 (ada0s1)
       partition "a" (ada0s1a, /)
       partition "b" (ada0s1b, swap)
       partition "d" (ada0s1d, /var)
       partition "e" (ada0s1e, /tmp)
       partition "f" (ada0s1f, /usr)
    MBR slice 2 (ada0s2)

Yes, one partition format inside another.  It only seems complicated 
because it is.

GPT is the new partitioning format, which makes things much simpler by 
being capable of up to 128 partitions in the standard configuration. 
With GPT, there is no reason to use BSD disklabels at all.

   disk ada0
     GPT partition 1 (ada0p1, bootcode)
     GPT partition 2 (ada0p2, /)
     GPT partition 3 (ada0p3, swap)
     GPT partition 4 (ada0p4, /var)
     GPT partition 5 (ada0p5, /tmp)
     GPT partition 6 (ada0p6, /usr)

Summary: "Dangerously dedicated" partitioning has no unique advantages. 
Use GPT when possible, use MBR/disklabel when necessary.

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