mdadm array doesn't assemble
 

I have a system running fc10 and am setting up a software RAID array using mdadm. I have an array working in RAID 5 with 5 disks but after a reboot (or the devices are stopped in some other way) the array will not assemble with mdadm --assemble and with mdadm --auto-detect it builds it with 4 disks and a spare.

Could someone help me out?

Also when I use --examine on a device, it says there is no superblock and tells me nothing.

Thanks.

Hi,

are all partitions on the disks type fd?
Does mdadm work when you use it with the disk names attached like
?

I did find one drive that was not raid autodetect (fd) and fixed that. I am trying a rebuild now but that will take a long time to check.

I also wonder, is there a way I may prevent my drives from getting new names whenever I swap some out? Having them get their device names at boot time is quite difficult when you have an array set up using a specific list of devices and perhaps you added a few drives or something.

Thanks more.

Hi,

take a search at google for devlabel. This will give persistent devicenames for disks across reboots and replacements.

Hi,

i found a nice description how devlabel works here.

When I try to rebuild with

mdadm --incremental --rebuild /dev/md0

it replies

no recognisable superblock on /dev/md0

Is there a way to rebuild the superblock or something?

Hi,

will add a device to an existing array. So i think your commandline is wrong, because you try to add /dev/md0 which is an existing array. Normally you would add additional disks to an array eg. for replacement.

?ok

What is the syntax to rebuild an array?

Do md arrays function like real RAID 5 (in my case)? Initially I was trying to test by building array, physically removing drive, and rebuilding... but after removal of drive I could still mount up? Twice. I think this is strange, it did some live rebuild, in 5 seconds, without asking? I don't really what's up.

And do you know what's going on with all my superblock errors? Whenever I try a command to modify or view array it tells me about how it can't read superblock. I can now assemble the array directly though.

For removal of a drive would I use:
mdadm --manage /dev/md0 --remove /dev/sdb1

Hi,

not sure if i all understand right :)

Sure you can mount your RAID-5 while one disk is gone. This is the purpose of RAID :) Yes md devices works like real RAID.

It's correct to remove a disk with --remove. Did you also have add a new disk or re-add an existing one? You can use --add to add a new disk or --re-add to add a disk previously removed.

The superblock errors occurs in case of incorrect usage. For example when you try to access the md-device istead of physical disk (in your --incremental for example you tried to access /dev/md0, but you have to use a physical devicename like /dev/sdb1).