[plug] dmraid vs mdadm

Sat Mar 3 20:54:42 WST 2012

Hi Tim

Thanks for your post. I tried this several times now, but everytime I boot of the Live CD I get md125 again. I have't been able to boot of hard drive as I keep on getting a kernel panic on boot up. I suspect the panic is caused by the kernel also not being able to find the correct md devices. I tried running the commands 
 mdadm -S /dev/md125
 mdadm -A /dev/md1 --update=super-minor
But they didn't fix the issue. Still on every reboot from LiveCD I get back to md125. After my initial installation after I created the file system on the raid array using :

mkfs.ext4 /dev/md1
mkswap /dev/md2
swapon /dev/md2
mkfs.ext4 /dev/md3

and a reboot, fdisk now reports that the partition table for mdX is not valid. 

Disk /dev/md127: 995.6 GB, 995640344576 bytes
2 heads, 4 sectors/track, 243076256 cylinders, total 1944610048 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x00000000

Disk /dev/md127 doesn't contain a valid partition table

Disk /dev/md126: 268 MB, 268369920 bytes
2 heads, 4 sectors/track, 65520 cylinders, total 524160 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x00000000

Disk /dev/md126 doesn't contain a valid partition table

Disk /dev/md125: 4294 MB, 4294901760 bytes
2 heads, 4 sectors/track, 1048560 cylinders, total 8388480 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x00000000

Disk /dev/md125 doesn't contain a valid partition table

I wonder why it is not picking up the partition table I created. 

I am using Gentoo for this as I really like it. It makes things a little bit more complicated but generally they work, well at least until now they did. 

On 03/03/2012, at 18:08 , Tim White wrote:

> Basically, linux will "auto assemble" raid devices it finds, even if they aren't for the current system. Annoyingly, it'll ignore the names the raid array say they want (/dev/md1, /dev/md2 etc) and give them numbers starting at 125. (Which can break a NAS if you plug in the raid drives into a normal machine, and don't set the names to the correct numbers before putting them back in the NAS).
> See https://bugzilla.novell.com/show_bug.cgi?id=638532#c1 for a solution to getting it to name them correctly and hopefully on reboot also named correctly.
> 
> What I'd do, boot off a live distro, assemble them with the correct numbers and update the preferred minor stuff (see above link), then mount them all and chroot into the system. From there, make sure that things like /etc/mdadm.conf are correct, and maybe even update your initramfs if needed.
> 
> I believe if you did a brand new OS install with an installer that supported setting up RAID as part of the install process, it would be simple. Which OS are you using? I understand that Debian should be fairly easy to get running on RAID.
> 
> Tim
> p.s. Stick with mdadm, it's much more portable when something breaks. As for how it works, that depends on it's RAID level, and yes, it's software RAID so no hardware accelerated RAID5 etc, I personally don't use RAID5 preferring RAID 0, 1 and 10. Drives are (were) cheap.
> 
> On 03/03/12 13:26, Alexander Hartner wrote:
>> 
>> I am setting up a new system. After partitioning /dev/sda, transferring my partition over to /dev/sdb using
>> 
>> sfdisk -d /dev/sda | sfdisk --force /dev/sdb
>> 
>> 
>> And setting up the raid arrays using :
>> 
>> mdadm --create --verbose /dev/md1 --assume-clean --level=1 -e 0.90 --raid-devices=2 /dev/sda1 /dev/sdb1
>> mdadm --create --verbose /dev/md2 --assume-clean --level=1 -e 0.90 --raid-devices=2 /dev/sda2 /dev/sdb2
>> mdadm --create --verbose /dev/md3 --assume-clean --level=1 -e 0.90 --raid-devices=2 /dev/sda3 /dev/sdb3
>> 
>> Everything seems OK, however if I reboot all the drive names change to :
>> 
>> cat /proc/mdstat 
>> Personalities : [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
>> md125 : active (auto-read-only) raid1 sdb1[1] sda1[0]
>>       262080 blocks [2/2] [UU]
>>       
>> md126 : active (auto-read-only) raid1 sdb2[1] sda2[0]
>>       4194240 blocks [2/2] [UU]
>>       
>> md127 : active (auto-read-only) raid1 sdb3[1] sda3[0]
>>       972305024 blocks [2/2] [UU]
>>       
>> unused devices: <none>
>> 
>> While this in itself may not be a problem, after I install my OS (Linux of course) I get a kernel panic. I suspect the kernel panic is due to the kernel not finding the partition I specified in grub.conf and fstab (i.e. : /dev/md1|2|3). 
>> 
>> I have been struggling with mdadm raid for several days now, with little progress to show. dmraid seems to leverage what little support is provided by my onboard RAID controller, which seems like a good think. mdadm seems to just keep both drives in sync with each other without leveraging hardware. I might well be wrong there. So far I only tried mdadm.
>> 
>> Alex
>> 
>> 
>> On 03/03/2012, at 09:33 , Marcos Raul Carot Collins wrote:
>> 
>>> Are you installing the OS or are you trying to implement to an extra hard disk 
>>> after installing?
>>> 
>>> I only set it up in Debian at install time (mdadm) and although you need some 
>>> partitioning background, it is prety easy. Let me know if that's your case and 
>>> I can guide you.
>>> 
>>> I haven't tried in other OSes...
>>> 
>>> Cheers,
>>> 
>>> Marcos
>>> 
>>> On Sábado 03 Marzo 2012 05:17:12 Tim White escribió:
>>>> On 03/03/12 04:36, Alexander Hartner wrote:
>>>>> Has anybody got any experience with either / both ? Which one do you
>>>>> suggest ? I have been trying to configure mdadm for the past week
>>>>> without success. Should I persist or try dmraid ? Is mdadm really so
>>>>> much better then dmraid ?
>>>> 
>>>> I've never used dmraid (and a quick read suggests it's for "software
>>>> raid" provided by certain bios).
>>>> What are you trying to achieve? I have successfully used mdadm many
>>>> times in the past, both with setting up raid and with repairing NAS's.
>>>> 
>>>> Tim
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>> 
>> 
>> 
>> _______________________________________________
>> PLUG discussion list: plug at plug.org.au
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> 

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