Re: [gentoo-user] Re: Duplicate identical Hard Disk

[Mark Knecht]

On Fri, Apr 2, 2010 at 9:37 AM, walt <w41ter@×××××.com> wrote:
> On 04/02/2010 07:59 AM, Mark Knecht wrote:
>
>>
>> 1) Yes, you can RAID partitions of drives. That's what I'm doing. You
>> can look at the Gentoo RAID/LVM Install guide to see an example of
>> using RAID0 and RAID1 on a single drive.
>>
>> http://www.gentoo.org/doc/en/gentoo-x86+raid+lvm2-quickinstall.xml
>
> Very useful post, thanks.  I'm just nitpicking here about the use of
> RAID0 on a single physical drive, which doesn't seem useful IIUC.
>
> RAID0 alternates stripes between two physical drives so that one disk
> can be reading/writing while the other disk's heads are seeking, no?
>
> If that is the case, then single-disk RAID0 will just be thrashing the
> heads back and forth between stripes on different partitions, making
> more work for itself than necessary.
>
> If I'm wrong about this, someone please correct me.

No, you are correct, RAID0 on a single drive makes no sense. If I
suggested that then I apologize for the confusion. I was only saying
that you can do RAID on one partition but do non-RAID on another. For
instance, /boot is non-RAID and then other partitions are RAID. I may
be wrong but I think that's only possible with software RAID. Not sure
you could do this behind a hardware RAID controller.

sda1 = /boot - non-RAID
sda2, sdb2, sdc2 = swap, but not RAID. The kernel binds them.
sda3, sdb3, sdc3 = RAID /home

or something like that.

In case even that's not clear, I don't think mdadm supports a RAID
array of any type with all the partitions on a single drive. For
instance:

mdadm --create /dev/md1 --level=1 --raid-devices=3 /dev/sda1 /dev/sda2 /dev/sda3

doesn't make any sense to me even if it is supported.

Hope that helps clear things up. ;-)

- Mark