On 13/08/2012 00:16, Rudy Zijlstra wrote:
Jonathan,
On 12-08-12 23:10, Jonathan Tripathy wrote:
Hi Everyone,
Our server currently has 6 SATA ports on the motherboard filled with
6 drives in RAID10. I have a need to install an additional PCIe SATA
controller in a server in order to obtain 2 more SATA ports to
install an additional 2 new drives (As I want a new RAID1 array).
However I would like to move one of the current drives onto the new
controller, and one of the new drives onto the motherboard. This
should give me a little redundancy in case the new controller card
were to fail (I don't want the new controller to bring down 2 drives).
When setting up MD RAID in this configuration, how would I go about
tell MD RAID which disk is which in the array (referring to the
near/far configurations)? I'm assuming by default that MD RAID just
uses alphabetical order in order to determine the drive order?
mdadm does not care about the disk ordering once the raid has been
defined. It uses the raid metadata on the disks to figure out which
disk is doing what. This includes which disk belongs to which raid.
There are 2 options:
- use metadata .90 (no longer suggested) and have the kernel
autodetect during boot
- use a later metadata (1.2 is default now), and have mdadm in the
initrd. This will use a config file that has mdadm search on UID.
Again, independent of which sdx the disks are.
You could test by swapping disk order in your current system. Although
i would suggest to do testing with a test machine ;)
Thanks for your reply.
Currently, we use CentOS and use the installer to set up the MD RAID. It
is using metadata version 0.90. The only thing in mdadm.conf is the UUID
of the array and the number of disks per array. It's good to know that
mdadm doesn't look as the sdx value once the RAID is setup. What I would
like to know is how to configure the disk order in the array. Or maybe
it's not very important to do this? For example, going by these
diagrams:
http://en.wikipedia.org/wiki/Non-standard_RAID_levels#Linux_MD_RAID_10
how do I know/configure which disk is A1 and which is A2? I just want to
know the disk order after i split my array across different adapters.
Thanks
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