Migrating to RAID 1 [SOLVED]

srunni · Guru Joined: 26 Dec 2007 Posts: 365

Hi,

I've got a system running on one 500 GB hard drive, and I'd like to migrate it to two 500 GB hard drives, running in RAID 1. I found this guide, but it has warnings about checking other information before attempting to migrate to RAID 1. Is there anything else that I need to read before I begin the migration? I have all my data backed up, but I'd like this to go smoothly if possible.

Thanks!

NeddySeagoon · Posted: Tue Aug 05, 2008 5:59 pm Post subject:

srunni,

That guide looks mostly harmless. The idea is this.
Using the new drive, you create your raid1 install in degraded mode.
Its very important you know which drive is which as you must only partition and make the raid sets on partitions belonging to the new drive. You tell mdadm that the raid1 partitions that will be on the existing drive are missing.

There is no need to make partitions on the new drive the same size as the old drive as you will use cp-a, rsync or whatever to copy files over.

Eventually, you have your old single drive install still running and a tested bootable raid1 install in degraded mode on the new drive.
The correct grub entries allow you to boot either. This is an important test. The next step wipes your single drive install.

Boot into the raid1 install, partition the old drive to match the new drive (with the raid install on) and add its partition to the working degraded raid to bring it up to full strenght. This is what you do to replace a failed drive too, so you get to practice at no extra charge.

If the degraded raid and single drive install get out of step while you are testing, because you allowed the single drive install to be used, for example, you need to fix the the differences before you migrate for real or the changes will be lost.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

srunni · Guru Joined: 26 Dec 2007 Posts: 365

wilf · Posted: Tue Aug 05, 2008 6:56 pm Post subject:

Hello srunni,

I like NeddiSeagoons comments - I run all my machines off software mirrors, although I have never converted as you are doing. I'd recommend you also have a look at HOWTO Install on Software RAIDwhich has an excellent section on Installing Grub onto both MBRs. This only becomes useful when your one and only boot drive fails :-)

You hopefully have partitioned your new drive with partitions as you wanted them of type fd, formatted the partitions, mounted them and copied over the data from your old drive, as per the HOWTO. Hence

NeddySeagoon · Posted: Tue Aug 05, 2008 7:24 pm Post subject:

srunni,

I didn't check the drive letters to know exactly what the

srunni · Guru Joined: 26 Dec 2007 Posts: 365

srunni · Guru Joined: 26 Dec 2007 Posts: 365

OK, I've started the process and I have some questions.

There are two main differences between my setup and the setup in the HOWTO.
1. I have a partition /dev/sdc, which has the existing data. I'm trying to copy it over to /dev/sdb, which is the new hard drive.
2. I have 4 partitions, instead of just one.

These are my questions:
1. Should I have /dev/md0 as the first RAID device even though the physical partition devices start at 1? I'm specifically referring to the command

NeddySeagoon · Posted: Wed Aug 06, 2008 8:41 am Post subject:

srunni,

In answer to your first 3 questions - yes.
Partition type 0xfd tells the kernel that the partition is part of a raid set, so it can be auto assembled during boot.

In the echo command, the syntax is correct - you need the ARRAY keyword but you need your own UUIDs, not the recurring deadbeef. (Thats a valid hex number by the way)
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

srunni · Guru Joined: 26 Dec 2007 Posts: 365

Yeah, I made sure I changed 'deadbeef'. Everything seems to be working now. Thanks for all your help!!