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Re: boot disk has two MBR partitions

On Sat, 23 Feb 2013, David Lord wrote:

On 23 Feb 2013 at 20:18, Saifi Khan wrote:


Please excuse me for asking rather 'naive' question.

i've rtfm'd at

Now, i have a boot disk (NetBSD terminology) of 320 GB (SATA II).

Booted my laptop with 'boot.iso' (NetBSD-current) and using the 'NetBSD' fdisk 
utility, i created two MBR partitions (NetBSD terminology) of the following 
 partition no 1: 20 GB   (base system, src)
 partition no 2: 300 GB (pkgsrc, other sources, mails etc.)

i intend to setup 'ffs' on both the MBR partitions.

in the linux world, the disk would typically be '/dev/sda' and the two profound 
partitions would be

in the NetBSD scheme of things, the first disk is seen as 'wd0'. In that case, 
how would the two 'MBR partitions' be addressed as ?

The NetBSD part of the disk is usually split into partitions

ID mount point
a: /
b: swap
c: NetBSD partitions
d: whole disk
e: /usr
f: /tmp
g: /var

The 'mbrlabel' command helped insert the 2nd MBR partition entry in the disklabel.

However, the wrong size was picked by mbrlabel (wonder why) and i had to edit the 'disklabel' entry from the information gleaned from 'fdisk' output.

Having many mountable partitions used to have an advantage
after a major system crash in that some would be left clean
which reduced time spent by fsck. With current WAPBL the
journal is replayed after a crash which gives a fast

Does disk geometry, the CHS remapping and subsequent translation have any impact on the 'fsck' performance. ?

i also have a couple of related questions:

1. what is the rationale behind using 'd' in BSD partition to represent the 
entire disk ?
2. what is the significance of using two representations like wd0 and rwd0 ?

The 'raw' devices have to be used in some cases but unless
you are sure use the 'wd" rather than "rwd".

Would appreciate, if you could share an example where 'raw' device would be useful.

3. does fsck like utility perform better when one has slice with BSD partitions 
rather than straight DOS like partition ?

DOS fat partitions become fragmented and can run out of
allocation units so require regular defragmentation as the
partition becomes full.

Fsck is not normally required on NetBSD ffs partitions.

currently running netbsd-current (20120220 snapshot).

i have had two freeze ups in the last 2 days, when i had to hold the 'power' button to switch off the laptop.

On power cycling the device, on both occassions, i had to run 'fsck' manually to restore blocks, clean up etc.


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