HOWTO: Linux Software Raid using mdadm

[alecm3]

Dear alecm3
Are you using Ubuntu Server? I know the respective kernels of desktop and server are different with server being more tweaked to perform server functionality as opposed to desktop.
Regards

Yes, I am using 8.04.1 hardy heron server...

[axcairns]

This is doing my head in. I created my array and can see it in mdstat but I can't get any partitions created on it. When I fdisk /dev/md0, create the partition and write I get the following -

Disk /dev/md0: 1000.2 GB, 1000210300928 bytes
255 heads, 63 sectors/track, 121601 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00048f36

    Device Boot      Start         End      Blocks   Id  System
/dev/md0p1               1      121601   976760001   83  Linux

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 22: Invalid argument.
The kernel still uses the old table.
The new table will be used at the next reboot.
Syncing disks.

Rebooting has no effect. The partition does not exist except inside fdisk! I checked /dev/disk/by-id/ and only the device itself (plus all the physical disks) was there. Opening fdisk again and the partition looks fine but exit and no sign.

/proc/mdstat

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
md0 : active linear sda1[0] sdb1[1]
      976767872 blocks 64k rounding
      
unused devices: <none>

/etc/mdadm/mdadm.conf

# mdadm.conf
#
# Please refer to mdadm.conf(5) for information about this file.
#

# by default, scan all partitions (/proc/partitions) for MD superblocks.
# alternatively, specify devices to scan, using wildcards if desired.
DEVICE partitions

# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes

# automatically tag new arrays as belonging to the local system
HOMEHOST <system>

# instruct the monitoring daemon where to send mail alerts
MAILADDR root

# definitions of existing MD arrays

# This file was auto-generated on Sat, 16 Aug 2008 14:15:06 +0800
# by mkconf $Id$

fdisk -l

Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x000d73fb

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1       60801   488384001   fd  Linux raid autodetect

Disk /dev/sdb: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x000d73fb

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1       60801   488384001   fd  Linux raid autodetect

Disk /dev/sdc: 40.0 GB, 40020664320 bytes
255 heads, 63 sectors/track, 4865 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x23eb23ea

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1   *           1        4678    37576003+  83  Linux
/dev/sdc2            4679        4865     1502077+   5  Extended
/dev/sdc5            4679        4865     1502046   82  Linux swap / Solaris

Disk /dev/sdd: 320.0 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x0c32b920

   Device Boot      Start         End      Blocks   Id  System
/dev/sdd1               1       38913   312568641   83  Linux

Disk /dev/md0: 1000.2 GB, 1000210300928 bytes
255 heads, 63 sectors/track, 121601 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00048f36

    Device Boot      Start         End      Blocks   Id  System
/dev/md0p1               1      121601   976760001   83  Linux

Disk /dev/sde: 320.0 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x44fdfe06

   Device Boot      Start         End      Blocks   Id  System
/dev/sde1               1       38913   312568641   83  Linux

Disk /dev/sdf: 320.0 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x41ffc810

   Device Boot      Start         End      Blocks   Id  System
/dev/sdf1               1       38913   312568641   83  Linux

Disk /dev/sdg: 320.0 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x44fdfe06

   Device Boot      Start         End      Blocks   Id  System
/dev/sdg1               1       38913   312568641   83  Linux

Help!

Allan

[axcairns]

Never mind - I'm an idiot. I was trying to partition the raid device rather than just formatting it.

[lleberg]

I followed the howto and set up 2x500 gb raid0, for storage.

Now i'm moving what i want to keep there, then i plan to format my system disc and reinstall.

But the thought just hit me, how do i do to add the raid array on the new system? is et as simple as i hope it is?

[crtlbreak]

You would need to obatin the alternate install CD I not he liveCD version. During the install process at disk config you will need to choose "custom" rather than just the defaults.You will then have the option to customise LVM, set up raid 0, 1, 5 etc.
Then the rest you should be quite used to.

[lleberg]

Oh, that's too bad, since i'm in my new system now.

And oh, i didn't use the actual howto o page one, but one linked to in the post, the one at http://www.linuxhomenetworking.com/w..._Software_RAID

Allthough i don't know the difference.

How do i go about to add the discs to the system?
Hopefully without destroying what's on them..

Edit:
Is it a bad idea to just recreate the raid array with

mdadm --create --verbose /dev/md0 --level=0 --raid-devices=2 /dev/sdb1 /dev/sdc1

Create the mdadm.conf Configuration File and
create a mounting point for it?
For me to acces the data written on both discs (stripe)

[cyberkost]

You would need to obatin the alternate install CD I not he liveCD version. During the install process at disk config you will need to choose "custom" rather than just the defaults.You will then have the option to customise LVM, set up raid 0, 1, 5 etc.
Then the rest you should be quite used to.

Well, yeah, but there's not much of "etc." there. E.g. level 10 is not available, so one has to do it "by hand."

[lleberg]

Problems solved, everyhnig is now fine.

The command i was looknig for was

sudo mdadm -A /dev/md0 /dev/sdb1 /dev/sdc1

[cyberkost]

I'm trying install Ubuntu-8.04 desktop following the instructions here: http://how2forge.org/install-ubuntu-...ftware-raid-10. Everything seems to be fine, but soon after I leave partitioner and go into "Installing system" window I get a error pop-up that says "The installer needs to remove operating system files from the install target, but was unable to do so. The install cannot continue."

Does anyone have any clue as to what might be happening?

Edit: I've done some poking around and it seems that the problem starts even earlier -- the partitioner does not see /dev/sdi, /dev/sdj, or /dev/sdk (that I have my /dev/md1, /dev/md2, and /dev/md3 aliased to). The only way I'm able to make partitioner see the raid partitions is to have them aliased (using -f option) to /dev/sd[e-g], which are SD, CF and MMS cardreaders on my system. SOS!!!

[crtlbreak]

I think that page actually has the answer for you

" ... Then create the file system on the RAID array. Format it now because the partitioner in the installer doesn't know how to modify or format RAID arrays. I used XFS file system, because XFS has great large file performance. Then you will create an alias for the RAID array with the link command because the Ubuntu installer won't find devices starting with "md"."

Does that seem logical?
Just to be sure - it is RAID 10 you are requiring with 4 seperate devices?