[Wylug-help] Inactive RAID 10 Array

[John Hodrien]

On Tue, 14 Apr 2009, Dave Fisher wrote:

> I suspect that the first thing I should do is dd sd{b,c,d,e}4 to some spare
> disks.

Fair enough.  How come the array's inactive when you've only lost one
partition?  What's happened to get you in this state?

> I currently have 3 spare 1TB SATA disks and am just about to pop out to
> buy 2 more, but before I do anything that relies on these spares I'd
> like to be more certain about how useful the dd'd copies are going to
> be, i.e. will they contain all the RAID metadata that I need to
> preserve?

Yes.

>  1. Some of the RAID metadata is stored elsewhere, e.g. on a different
>  partition or superblock.

Where would it store it?

>  2. There may be hardware constraints that I've forgotten or never knew
>  about.

It's software RAID, so there's no hardware constraints.  That's one of the
clear wins of software RAID.

>     For example, I remember that the partitions in an array have to be
>     identically sized, but I am guessing that they don't have to be
>     physically identical, i.e.  they don't have to occupy identically
>     positioned blocks on identical models of HDD.

No.

>     So I should be able to treat raw images of the partitions just like the
>     originals.
>
>     Is this the case?

I've no tried swraid with partition images, but I don't see any reason why
not.

>     What about block sizes for the dd'd copies?

A bigger block size than the default would be much faster.

>     Would this command be sufficient to copy /dev/sdb4?
>
>       $ sudo dd if=/dev/sdb4 of=/dev/sdg

Why switch from a partition to a whole disk?  But yes, my understanding is
that would work fine.

jh

-- 
"People who get up early in the morning cause war, death and famine"
                                                      -- Banksy