[mythtv-users] OT Help: mdadm segfault

[Steve MacLaren]

On 9/21/07, Steve MacLaren <scram69 at gmail.com> wrote:
>
>
>
> But it looks like I will just have to ignore the obvious contradictions
> and forge ahead trying to mount and access a 3-drive array by messing with
> /sys/block/md0/md/array_state, then wiping and re-adding the fourth drive...
>
>

Finally, some good news.  Before I went ahead picking 3 disks at random and
assembling, I re-read through all of the posts on this thread.  The one that
caught my eye was in f-myth's PPS:
"for each drive, try dd if=/dev/sdaN of=/dev/null bs=1M count=1000 and see
if you can read the first gig of the device"
I hadn't yet tried that, so I gave it a try.  Sure enough, /dev/sdd1 cause a
reboot when I tried the read.  Not being hardware-savvy enough to know which
of my physical drives was _actually_ /dev/sdd, I ran through a process of
elimination, removing power to one drive at a time until I could
successfully read from the three remaining drives.
Identifying the bad drive, I yanked it, replaced it with a brand new spare I
had fortuitously purchased some months ago, and restarted.
Upon restart, in dmesg, mdadm gave the same complaints about "dirty" drives
and the array status remained inactive.  But I tried
mdadm -S /dev/md0
mdadm -Af /dev/md0 /dev/sda1 /dev/sdb1 /dev/sdc1
"mdadm: /dev/md0 has been started with 3 drives (out of 4)." - hey, that
looks good!

So, next,
sudo mdadm --detail /dev/md0
"...
 State : clean, degraded"

I don't feel so dirty anymore...

Pushing my luck,
sudo mount -t xfs /dev/md0 /var/lib/mythtv
and all of my data was back, seemingly intact!

So I did an fdisk on the new disk, formatting it as "linux raid autodetect",
then:
steve at mediaserver:~$ sudo umount /dev/md0
steve at mediaserver:~$ sudo mdadm -a /dev/md0 /dev/sdd1mdadm: added /dev/sdd1
steve at mediaserver:~$ sudo mdadm --detail /dev/md0
/dev/md0:
        Version : 00.90.03
  Creation Time : Mon May  7 21:31:55 2007
     Raid Level : raid5
     Array Size : 1465151616 (1397.28 GiB 1500.32 GB)
    Device Size : 488383872 (465.76 GiB 500.11 GB)
   Raid Devices : 4
  Total Devices : 4
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Fri Sep 21 23:24:58 2007
          State : clean, degraded, recovering
 Active Devices : 3
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 1

         Layout : left-symmetric
     Chunk Size : 128K

 Rebuild Status : 0% complete

           UUID : bc7a4d90:bd286a91:c109596b:d7e29b7e (local to host
mediaserver)
         Events : 0.174

    Number   Major   Minor   RaidDevice State
       0       8        1        0      active sync   /dev/sda1
       1       8       17        1      active sync   /dev/sdb1
       2       8       33        2      active sync   /dev/sdc1
       4       8       49        3      spare rebuilding   /dev/sdd1

Success!  Thanks to everyone who helped me through this special hardware
hell nightmare!
Now I can finally get back to troubleshooting my "ivtv driver has stopped
responding" errors...
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