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Old 07-09-2013, 09:08 PM   #1
Scrapper64
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Registered: Jul 2012
Location: Metro-Atlanta
Distribution: CentOS & Fedora
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Move Raid-1 Array From Server B to Server A


On Server B I lost my motherboard due to a power surge while I had the box off of my UPS.

I really, really want to recover the data on the hard drives, so here's my situation:

Machine A has 4 - 1 TB SATA hard drives configured Raid-1 and showing Raid-1 partitions /dev/md0 through /dev/md7. With /dev/md0 being a regular partition for /boot, with /dev/md1 through /dev/md7 defined as volume groups.

Machine B had 2 - 1.5 TB SATA hard drives configured Raid-1 and showing Raid-1 partitions /dev/md0 through /dev/md6. With /dev/mdo being a regular partition for /boot, with /dev/md1 through /dev/md6 defined as volume groups.
I moved these drives from machine B to machine A and booted machine A and got the following:

The machine booted normally but when I did a fdisk -l it showed the new drives as /dev/hda and /dev/hdb but all of the define partitions were there as they should be, even the one showing it wasn't on a cylinder boundary. All of the partitions showed up as type 8e as they should. I decided not to worry why the drives weren't /dev/sde and /dev/sdf and entered the following command from the command line:
mdadm --manage add /dev/md8 /dev/hda1
I got the following message:
'Device /dev/md8 cannot be found'

I did a ls -ltr /dev/md* and sure enough it wasn't there.

I guess to start my questions are:
1. Why are the disk showing up as /dev/hda and /dev/hdb?
2. How do I create /dev/md8?
3. What is the maximum number of the /dev/md?
4. Is there a better way of doing this?

TIA
Scrapper64
 
Old 07-09-2013, 11:23 PM   #2
smallpond
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The md and hd numbers have no meaning other than the order that the drives and arrays are found at boot. That's OK because md reassembles the RAID arrays by drive UUID, which doesn't change. You should never use the md, sd or hd names in fstab. Mount by UUID or logical volume name.

You can list the known arrays with the command:

Code:
cat /proc/mdstat
Most likely your arrays are there, just with new names. If not, use mdadm to find and assemble them.

Note: there is no such thing as a cylinder boundary. fdisk should know better.
 
1 members found this post helpful.
Old 07-10-2013, 10:06 PM   #3
Scrapper64
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Registered: Jul 2012
Location: Metro-Atlanta
Distribution: CentOS & Fedora
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Move Raid-1 Array From Server B to Server A

Thanks for the tip on mdadm. I just need to teach myself the mdadm command. Anyone know of a good mdadm tutorial?

I also found out why those 2 drives are designated as /dev/hda and /dev/hdb - it's because 2 of the SATA ports are SATA/IDE combination. I have been assured by the motherboard manufacture that everything will work as expected.
 
  


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