Subject: Re: RAIDframe documentation concerns
To: NetBSD port-sparc64 mailing list <port-sparc64@netbsd.org>
From: Julian Coleman <jdc@coris.org.uk>
List: port-sparc64
Date: 10/24/2005 13:53:16
> 2.  The reason for choosing a particular dumpdev partition size is not
>     stated in the RAIDframe documentation and I believe it should be.
>     It is stated in swapctl(8); however, I believe that there are some
>     users who will not know how to properly select a size for this
>     partition and may select one which is too small.  I believe the
>     RAIDframe documentation should be modified to state that the
>     dumpdev partition size should be equal to or larger than than the
>     amount of physical memory the computer has installed.

This is the case with or without raid.  However, perhaps the RAIDframe
section could refer to other sections/manual pages?

>     Furthermore, I believe it would be wise to caution users that they
>     may wish to consider the maximum amount of physical memory their
>     computer can accommodate and consider the likelihood of an upgrade
>     that would cause their dumpdev partition to be undersized.  Do I
>     correctly understand dumpdev size selection?  Should these
>     concerns be included in the RAIDframe documentation?

Again, I think this is more general.  However, the one item specific to
RAIDframe is having separate swap and dump partitions.

Also, you can save disk space by overlapping the raid swap device and
the dump device on the underlying disk (I can't remember who pointed
this out previously).  For example, I have (on a U5):

  disklabel sd0:
#        size    offset     fstype [fsize bsize cpg/sgs]
 a:  35368272         0       RAID                     # (Cyl.      0 -   7505)
 d:   1050776   4198392       swap                     # (Cyl.    891 -   1113)

  disklabel raid0:
#        size    offset     fstype [fsize bsize cpg/sgs]
 a:   4195328         0     4.2BSD   2048 16384 21872  # (Cyl.      0 -   4096)
 b:   2098176   4195328       swap                     # (Cyl.   4097 -   6145)

  fstab:
/dev/raid0b     none            swap    sw      0       0
/dev/sd0d       none            dump    dp      0       0

The offset of raid0c from the beginning of sd0c is 64 sectors, so as long
as the dump partition starts after (raid0b offset + 63) and ends before
(raid0b offset + raid0b size + 64), you'll be fine.  You can test that
you've got it right by using dd to write to the start and end sectors of
sd0d and to read from the corresponding sectors in raid0b (whilst single
user).

J

-- 
  My other computer also runs NetBSD    /        Sailing at Newbiggin
        http://www.netbsd.org/        /   http://www.newbigginsailingclub.org/