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Recovering from a dead disk in a Linux software-RAID5 system using mdadm

RAID5 failure

As I wrote quite a while ago, I set up a RAID5 with three
IDE disks at home, which I'm using as backup (yes, I know that
RAID != backup) and storage space.

A few days ago, the RAID was put to a real-life test for the first time, as one of the disks died. Here's what that looks like in dmesg:

raid5: raid level 5 set md1 active with 3 out of 3 devices, algorithm 2
RAID5 conf printout:
 --- rd:3 wd:3
 disk 0, o:1, dev:hda2
 disk 1, o:1, dev:hdg2
 disk 2, o:1, dev:hde2
[...]
hdg: dma_timer_expiry: dma status == 0x21
hdg: DMA timeout error
hdg: 4 bytes in FIFO
hdg: dma timeout error: status=0x50 { DriveReady SeekComplete }
ide: failed opcode was: unknown
hdg: dma_timer_expiry: dma status == 0x21
hdg: DMA timeout error
hdg: 252 bytes in FIFO
hdg: dma timeout error: status=0x50 { DriveReady SeekComplete }
ide: failed opcode was: unknown
hdg: dma_timer_expiry: dma status == 0x21
hdg: DMA timeout error
hdg: 252 bytes in FIFO
hdg: dma timeout error: status=0x58 { DriveReady SeekComplete DataRequest }
ide: failed opcode was: unknown
hdg: DMA disabled
ide3: reset: success
hdg: dma_timer_expiry: dma status == 0x21
hdg: DMA timeout error
hdg: 252 bytes in FIFO
hdg: dma timeout error: status=0x58 { DriveReady SeekComplete DataRequest }
ide: failed opcode was: unknown
hdg: DMA disabled
ide3: reset: success
hdg: status timeout: status=0x80 { Busy }
ide: failed opcode was: 0xea
hdg: drive not ready for command
hdg: lost interrupt
hdg: task_out_intr: status=0x50 { DriveReady SeekComplete }
ide: failed opcode was: unknown
hdg: lost interrupt
hdg: task_out_intr: status=0x50 { DriveReady SeekComplete }
ide: failed opcode was: unknown

That's when I realized that something was horribly wrong.

Not long after that, these messages appeared in dmesg. As you can see the software-RAID automatically realized that a drive died and removed the faulty disk from the array. I did not lose any data, and the system did not freeze up; I could continue working as if nothing happened (as it should be).

 md: super_written gets error=-5, uptodate=0
 raid5: Disk failure on hdg2, disabling device.
 raid5: Operation continuing on 2 devices.
 RAID5 conf printout:
  --- rd:3 wd:2
  disk 0, o:1, dev:hda2
  disk 1, o:0, dev:hdg2
  disk 2, o:1, dev:hde2
 RAID5 conf printout:
  --- rd:3 wd:2
  disk 0, o:1, dev:hda2
  disk 2, o:1, dev:hde2

This is how you can check the current RAID status:

 $ cat /proc/mdstat
 Personalities : [raid6] [raid5] [raid4] 
 md1 : active raid5 hda2[0] hde2[2] hdg2[3](F)
       584107136 blocks level 5, 64k chunk, algorithm 2 [3/2] [U_U]

The "U_U" means two of the disks are OK, and one is faulty/removed. The desired state is "UUU", which means all three disks are OK.

The next steps are to replace the dead drive with a new one, but first you should know exactly which disk you need to remove (in my case: hda, hde, or hdg). If you remove the wrong one, you're screwed. The RAID will be dead and all your data will be lost (RAID5 can survive only one dead disk at a time).

The safest way (IMHO) to know which disk to remove is to write down the serial number of the disk, e.g. using smartctl, and then check the back side of each disk for the matching serial number.

 $ smartctl -i /dev/hda | grep Serial
 $ smartctl -i /dev/hde | grep Serial
 $ smartctl -i /dev/hdg | grep Serial

(ideally you should get the serial numbers before one of the disks dies)

Now power down the PC and remove the correct drive. Get a new drive which is at least as big as the one you removed. As this is software-RAID you have quite a lot of flexibility; the new drive doesn't have to be from the same vendor / series, it doesn't even have to be of the same type (e.g. I got a SATA disk instead of another IDE one).

Insert the drive into some other PC in order to partition it correctly (e.g. using fdisk or cfdisk). In my case I needed a 1 GB /boot partition for GRUB, and the rest of the drive is another partition of the type "Linux RAID auto", which the software-RAID will then recognize.

Then, put the drive into the RAID PC and power it up. After a successful boot (remember, 2 out of 3 disks in RAID5 are sufficient for a working system) you'll have to hook-up the new drive into the RAID:

 $ mdadm --manage /dev/md1 --add /dev/sda2
 mdadm: added /dev/sda2

My new SATA drive ended up being /dev/sda2, which I added using mdadm. The RAID immediately starts restoring/resyncing all data on that drive, which may take a while (2-3 hours, depends on the RAID size and some other factors). You can check the current progress with:

 $ cat /proc/mdstat 
 Personalities : [raid6] [raid5] [raid4] 
 md1 : active raid5 sda2[3] hda2[0] hde2[2]
       584107136 blocks level 5, 64k chunk, algorithm 2 [3/2] [U_U]
       [>....................]  recovery =  0.1% (473692/292053568) finish=92.3min speed=52632K/sec

As soon as this process is finished you'll see this in dmesg:

 md: md1: recovery done.
 RAID5 conf printout:
  --- rd:3 wd:3
  disk 0, o:1, dev:hda2
  disk 1, o:1, dev:sda2
  disk 2, o:1, dev:hde2

In /proc/mdstat you'll see "UUU" again, which means your RAID is fully functional and redundant (with three disks) again. Yay.

 $ cat /proc/mdstat
 Personalities : [raid6] [raid5] [raid4] 
 md1 : active raid5 sda2[1] hda2[0] hde2[2]
       584107136 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]

Btw, another nice utility you might find useful is hddtemp, which can check the temperature of the drives. You should take care that they don't get too hot, especially so if the RAID runs 24/7.

 $ hddtemp /dev/hda
 dev/hda: SAMSUNG HD300LD: 38 °C
 $ hddtemp /dev/hde
 dev/hde: SAMSUNG HD300LD: 44 °C
 $ hddtemp /dev/sda
 dev/sda: SAMSUNG HD322HJ: 32 °C

Running homebrew and open-source software on your Wii, using the Twilight Hack and the Homebrew Channel

Wii

I've been owning a Nintendo Wii for quite a while now, but so far only played an occasional game of tennis or the like. Over the holidays I got The Legend of Zelda: Twilight Princess, which is a really nice game in itself. What is even more interesting though, is that this game allows you to run homebrew software on your Wii.

What you usually want to do, is to use the so-called Twilight Hack to install the Homebrew Channel on your Wii (you'll need an SD card and the Twilight Princess game for this). Once the process has finished you won't need the game anymore though.

So, here's a quick tutorial on how to install the Homebrew Channel. I basically followed the Setting up your Wii for Homebrew HOWTO from wiibrew.org.

Requirements

An SD card max. 2GB in size (not an SDHC card!), an SD card reader in your PC or laptop, and the Twilight Princess game (which you must play at least once).

Backup

First, you'll want to backup your Twilight Princess save games (if any). For that, we format the SD card (it needs a FAT16/FAT32) filesystem.

 $ mkfs.vfat /dev/mmcblk0p1 (you may need to change "mmcblk0p1" to whatever fits your setup)

Now insert the SD card into the Wii, start the Wii, go to Wii Options --> Data Management --> Save Data --> Wii and copy your Twilight Princess save games onto the SD card. Then, poweroff, remove the SD card, insert it into your laptop/PC and copy the save games to a safe place.

 $ mount -t vfat /dev/mmcblk0p1 /mnt
 $ mv /mnt/private ~/zelda_savegames

Twilight Hack and Homebrew Channel

The Legend of Zelda: Twilight Princess

Next up: download the Twilight Hack and Homebrew Channel, and put the files on the SD card:

 $ wget http://hbc.hackmii.com/dist/twilight-hack-v0.1-beta1.zip
 $ unzip twilight-hack-v0.1-beta1.zip
 $ cp -r private /mnt
 $ wget http://hbc.hackmii.com/dist/the_homebrew_channel-1.0.1.tar.gz
 $ tar xfvz the_homebrew_channel-1.0.1.tar.gz
 $ cp the_homebrew_channel-1.0.1/boot.dol /mnt
 $ umount /mnt

Now remove the SD card, insert it into the Wii and power-up the Wii. Go to Wii Options --> Data Management --> Save Data --> Wii, delete the Wii Twilight Princess save games, then copy the "Twilight Hack" save game from the SD card onto the Wii (you need to select the correct one for your region).

Quit the menu, start Twilight Princess, load the "Twilight Hack" savegame and finally talk to the person in front of you (do not perform any other actions, or the Wii may crash!). Follow the remaining instructions on the screen and you're done. You now have an additional channel named Homebrew Channel where all your homebrew programs/games (and your own Free Software programs you may write/port) will appear.

Installing homebrew software

So far, there are no real applications in the Homebrew Channel, you need to put all the homebrew software you want on the SD card. There's a huuuge list of applications and games to choose from, many of them Free Software with source code, some however are binary-only.

Basically, you put each application in a sub-directory of apps/ on the SD card, the most important file in every sub-directory is always boot.dol. If you have a boot.elf file instead, you'll probably need to convert it using the ELF to DOL converter.

Restoring Twilight Princess save games

You may now want to restore your Twilight Princess save games onto the Wii, you no longer need the "Twilight Hack" save game. Put your ~/zelda_savegames directory on the SD card and name it private/ again. Insert the SD card into the Wii and copy the save games on the Wii (similar procedure as above).

Have fun with homebrew software on your Wii, or even better write your own software or port existing Linux applications/games!

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