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Old 12-11-2008, 02:45 PM   #1
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CentOS 5.2 Mirrored RAID error and general question

Please bear with me as I try to figure this out. RAID is new to me and I might ask some really basic questions. Explanation first... Questions are at the end if you want to skip to that. Here goes...

I just built a new 64-bit system with a SATA RAID controller on board. I went in through BIOS and set up the two disks (Identical Western Digital 500GB drives) as a being a mirrored RAID array. After going through the install for CentOS, it automatically recognized the RAID and partitioned the drives to default. Based on this, I assume that I have a hardware RAID setup (as opposed to a software RAID)???

Anyways, the system setup fine. Both disk lights would flash every time there was activity, leading me to believe that information was being copied on both disks. After everything was working, I turned off the machine and pulled out one of the disks. I popped in another identical one and wanted to see if the RAID would pick it up. I start up the system and it recognizes the new drive, sets the system to rebuild, and then says that the rebuild will occur once I get into the OS. Umm... okay. I exit, the OS starts to load and all of a sudden I'm sent back to the initial setup page (time settings, users, etc). I log in and everything I added is gone! The rebuild never kicks in, so I shut down, replace the working disk with the other RAIDed one (so now I have the blank one still and the other mirrored disk in). I turn on the system. BIOS RAID recognizes the disk as Degraded and the blank one as Failed. I exit and go to load the OS. Now everything is back. All the programs I had set up and users are all there.

So... Does this mean the RAID never really worked?
The information wasn't truly copied onto both drives?
If it's truly mirrored, why would one disk work fine and the other not at all? It makes me worry that if the wrong disk fails, how am I supposed to truly rebuild the system?
Did I do something wrong when I initially setup the partitions?

Any help would be greatly appreciated. Thanks for taking the time.
Old 12-11-2008, 04:52 PM   #2
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If things are being written to both disks, then it seems likely that you have some sort of working RAID setup. It would help to know which drives the system sees as being used; could you post your /etc/mtab file?

If the system booted on one disk and not the other one, then it seems likely that you only have a bootloader (most likely GRUB) installed on only one of the disks, and it's only using the RAID setup for the root filesystem. It shouldn't be too hard to install grub on each disk, although you may need to do this periodically if your installer changes with system updates.

These instructions are for software RAID, but installing the bootloader should work in the same way:
Old 12-11-2008, 05:27 PM   #3
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# cat /etc/mtab

/dev/mapper/VolGroup00-LogVol00 / ext3 rw 0 0
proc /proc proc rw 0 0
sysfs /sys sysfs rw 0 0
devpts /dev/pts devpts rw,gid=5,mode=620 0 0
/dev/sda1 /boot ext3 rw 0 0
tmpfs /dev/shm tmpfs rw 0 0
none /proc/sys/fs/binfmt_misc binfmt_misc rw 0 0
sunrpc /var/lib/nfs/rpc_pipefs rpc_pipefs rw 0 0

So... It looks like /boot is ONLY run off of /dev/sda1... That doesn't sound like it's a true mirrored disk then. That doesn't make sense to me. Is there something I can do when I install CentOS to ensure that the disks are REALLY mirrored? It defeats the purpose of having RAID setup if you have to do manual work to ensure that a disk crash won't bring the system back up... I have the liberty of starting over as I'm still in the testing phase of putting these servers out. Any recommendations for the best approach to setting a mirrored RAID within my particular system?

Thanks again for all your help. I really do appreciate it.

Old 01-07-2009, 01:36 PM   #4
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I am currently running into the same situation with a NVidia RAID 5 controller on board - the MediaShield BIOS shows it is configured correctly and is giving the correct available space, it is also set to bootable. When CentOS installer pops up it complains about an immediately error:

"Error opening /dev/mapper/nvidia_bjefejjj: No such device or address"

It seems there is a work around using fakeraid, but this guide is only for Ubuntu.

It seems that CentOS doesn't know the RAID controller? Is there a way to for this to work?


centos, controller, fakeraid, nvidia, raid

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