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Old 08-06-2010, 03:42 PM
tormen
 
Default Questions about dm-raid isw (device naming and partition table)

Hi everybody,

I am new to dm-raid and have a couple of questions regarding how it works
(specifically regarding the device naming and access to the partition
table).

Any answer (or references to documentation) would be great!

Before I start with my questions: A short description of my use case for
dm-raid isw:

I am having a notebook with a RAID-0 (stripe) intel fake hardware raid
(on 4 sata devices ).

Out of the box (setup by the manufacturer - with Win7) when starting
with the linux rescue cd (that used dm-raid isw),
I got these partitions:
dm-0 (seemed to be everything == the 4 drives combined)
dm-1 (primary partition)
dm-2 (primary partition, active)
dm-3 (primary parition)

After repartioning (with linux based acronis disk-director that also
uses dm-raid isw)
now I have:
dm-0, dm-1, ... dm-10 where dm-0 still seems to be the WHOLE
raid-disk and dm-1 to dm-10 represent the 10 partitions (logical and/or
primary).

//////////////////////////////////////////////////////////////////////////////////////////////////////////////

/1st/ question:
With dm-raid isw and 1 RAID: dm-0 is everything (like the whole virtual
(raid) disk)?

/2nd/ question:
Can I use cfdisk to access the parition table / view the partioning
under linux?
... because when I try
cfdisk /dev/dm-0
I get this error message:
"FATAL ERROR: Bad primary partition 1: Partition ends in the
final partial cyllinder
And the same when I try to print the partition table with cfdisk.

If I start cfdisk -z /dev/dm-0 it works and could (from scratch)
partition the raid-drive.
But I noticed that then the partitions seem to be called dm-0p1, dm-0p2
(I hope I recall the naming correctly).

/3rd/ question:
Why would the partitions be called dm-0p1, dm0p2, ... within cfdisk
while otherwise I see dm-1, dm-2, ... ?
What is the difference between dm-0p1 and dm-1?

/4th/ question:
So regardless of logical / primary partitions the devices are always
named consecutively (1, 2, 3...)?
(in contrast to: /dev/sda1.../dev/sda4 beging primary paritions and
/dev/sda5 being the first logical partition)

/5th/ question:
Is there a way to partition the raid (e.g. with cfdisk) under linux
(without using third party software like acronis) so that Win7 and Linux
can access the raid-drive / partition table ((and don't complain about
fatal errors))?

/6th/ question:
Does the "partition 1" from the above cfdisk fatal error message refer
to /dev/dm-1
(because that is the 1st partition on the raid device /dev/dm-0) or what
partition / device
does it refer to?

Thanks a lot in advance for any hint / advise!

Best,

Knuth

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