Migrating a RAID to a new motherboard

[Franc Zabkar]

I have no RAID experience, so what I'm asking may appear trivial. What
are the precautions one should observe when migrating a RAID to a new
motherboard?

AIUI, the RAID controller mantains metadata (eg stripe size, drive
order) on the drives themselves, and the format of these metadata is
not necessarily consistent between controllers and chipsets.

I would think that the safest method would be to install the RAID
members as a JBOD, and then use a utility such as DMDE or mdadm
(Linux) to reconstruct the RAID. In DMDE you would examine sector 0 to
locate the MBR. This would be the first member of a RAID 0, for
example. Then one could experiment with stripe size until the data
were visible.

At this point you would backup your data. Then you could reconfigure
your drives as a RAID via the controller's BIOS extensions.

- Franc Zabkar

 

[Arno]

I have no RAID experience, so what I'm asking may appear trivial.

In theory, yes. In practice, a definitive no. This has a really
high likelyhood for going wrong, especially if you do it
for the first time.

What
are the precautions one should observe when migrating a RAID to a new
motherboard?

A full, verified backup! Otherwise you get what you deserve,
namely a really high probability of complete data loss.

AIUI, the RAID controller mantains metadata (eg stripe size, drive
order) on the drives themselves, and the format of these metadata is
not necessarily consistent between controllers and chipsets.

It typically is not. And it gets worse: Some controllers maintain
the metadata not on disk but in on-board flash.

I would think that the safest method would be to install the RAID
members as a JBOD, and then use a utility such as DMDE or mdadm
(Linux) to reconstruct the RAID. In DMDE you would examine sector 0 to
locate the MBR. This would be the first member of a RAID 0, for
example. Then one could experiment with stripe size until the data
were visible.

mdadm would not work. The metadata format is not standardized
and every vendor does its own thing. Sometimes vendors are
not compatible to themselves. The metadata placement or size is
also not standardized. Maybe dmraid would work, it can
use some vendor metadata formats.

At this point you would backup your data. Then you could reconfigure
your drives as a RAID via the controller's BIOS extensions.

You should always make backup the first step. It is not so
unlikely that you will damage something when you move the disks
over. You could also make a mistake when trying to reassemble
the RAID. With your proposes approach you would have to be very,
very careful not to write to the RAID for example.

Arno

 

[Franc Zabkar]

It typically is not. And it gets worse: Some controllers maintain
the metadata not on disk but in on-board flash.

I was watching a thread in another storage forum where a member
mentioned DDF. Apparently DDF is an attempt to standardise RAID
metadata. It stores these data on the drive, at the very end.

Common RAID Disk Data Format (DDF) Specification v2.0
http://www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf

Common RAID Disk Data Format (DDF) v1.2:
http://www.snia.org/sites/default/files/SNIA-DDFv1.2_with_Errata_A_Applied.pdf

"The Common RAID Disk Data Format specification defines a standard
data structure describing how data is formatted across the disks in a
RAID group. The Disk Data Format (DDF) structure allows a basic level
of interoperability between different suppliers of RAID technology.
The Common RAID DDF structure benefits storage users by enabling
data-in-place migration among systems from different vendors."

"The Anchor Header for the DDF structure MUST be stored at the last
logical block returned by either the ATA Identify Device or SCSI Read
Capacity commands depending on the type of physical disk.

The DDF structure SHOULD be stored at the end of the physical disk
next to the anchor header. Storing the DDF structure at the end of the
physical disk allows the possibility of converting a single non-RAID
physical disk to a RAID 1 configuration without shifting user data.
Similarly, data on a member of a RAID 1 configuration with the DDF
structure at the end can also be accessed using a non-RAID
controller."

- Franc Zabkar

 

[Man-wai Chang]

I have no RAID experience, so what I'm asking may appear trivial. What

are the precautions one should observe when migrating a RAID to a new
motherboard?

BACK UP FIRST!!

I would think that the safest method would be to install the RAID
members as a JBOD, and then use a utility such as DMDE or mdadm
(Linux) to reconstruct the RAID. In DMDE you would examine sector 0 to
locate the MBR. This would be the first member of a RAID 0, for
example. Then one could experiment with stripe size until the data
were visible.

I upgraded my motherboard with RAID 0 from Asus M2N-E to Asus M3N78-PRO,
and I found that M3N78-PRO could see the RAID 0 of M2N-E without loading
a new driver. I suspect for the same family of chipset, you possibly
don't even need to re-install your Window$.

Anyway, DO NOT gamble! Always back up your valuable data.

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[Tom Del Rosso]

A full, verified backup! Otherwise you get what you deserve,
namely a really high probability of complete data loss.

I would do at least 2 backups using 2 different backup devices. It's
consistent with the use of RAID to use 2 backup drives.