Re: A few remaining questions about installing to RAID-10

["Keld Jørn Simonsen" <keld@dkuug.dk>]

On Fri, Oct 02, 2009 at 07:54:04AM -0700, Ben DJ wrote:
> Hi everybody,
> 
> 2009/10/2 Keld Jørn Simonsen <keld@dkuug.dk>:
> > You can boot from a raid-10,n2 with the superblock last, standard
> > raid10,n2 will do. But the normal thing is to boot from raid-1
> >
> > There is a description of a setup at
> > http://linux-raid.osdl.org/index.php/Preventing_against_a_failing_disk
> 
> Thanks for the URL.  Is there a reason that raid-1 is the "normal
> thing"? Just popularity or something technical?

it is because raid1 is what traditionally worked. raid10,n2 will not work
in some situations.  raid10 is "new" and "dangerous" (FUD). Many people
do not know about raid10, and its wonders.

> In your reference it says "The root file system can be on another raid
> than the /boot partition. We recommend an raid10,f2, as the root file
> system will mostly be reads, and the raid10,f2 raid type is the
> fastest for reads, while also sufficiently fast for writes. Other
> relevant raid types would be raid10,o2 or raid1." and "a small /boot
> partition. We recommend something like 200 MB on an ext3 raid1".
> 
> How or why did you arrive at "raid-10,n2 with the superblock last"?

what lilo and grub really do is that they just read from one disk, so if
the raid type happens to be the same layout as  a non-raid partition, it
works. raid10,n2 default layout (ver 0.90) is equivalent with non-raid,
as the raid superblock is in the end of the partition. I understand that
other versions of the superblock are put other places, such as in the
beginning of the partition.

best regards
keld
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