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After having to reinstall the OS I am having trouble accessing data stored on a RAID5 group built on 8 HDDs using mdraid. Advice much appreciated!

I have a DIY home NAS server built on Intel Atom (Zotac NM10-DTX WiFi), 8 x 2TB WD Caviar HDDs connected via a HighPoint-RocketRAID 2680, as well as a 64GB SSD for the OS.

The setup was running fine for nearly 2 years (on Ubuntu Server 10.4 LTS) and using mdraid (it turned out I could get better performance using the RAID adapter only for connecting the drives and using mdraid to build a 14TB RAID5 array).

I recently started to experience some performance issues (reads and writes became slow - both when accessing the data from other hosts in my network and also running dd locally on the NAS server) so I decided to update the OS at it's been a while (I only had automatic security updates). The update went horribly wrong with the OS not even booting after the update - so I decided to make a clean install of Ubuntu Server 12.04.

Thanks to askubuntu I managed to build the driver for the RocketRAID 2680 and I can see all 8 drives (/dev/sdb through /dev/sdi) and running mdadm --examine returns:

/dev/sdb1:
Magic : a92b4efc
Version : 0.90.00
UUID : e667bd7d:d55be409:e9e4094c:aa5ad989 (local to host wega)
Creation Time : Wed Jan  5 16:47:34 2011
Raid Level : raid5
Used Dev Size : 1953431232 (1862.94 GiB 2000.31 GB)
Array Size : 13674018624 (13040.56 GiB 14002.20 GB)
Raid Devices : 8
Total Devices : 8
Preferred Minor : 0

Update Time : Tue Oct 15 18:36:41 2013
State : clean
Active Devices : 8
Working Devices : 8
Failed Devices : 0
Spare Devices : 0
Checksum : d1fdf40 - correct
Events : 1010

Layout : left-symmetric
Chunk Size : 64K

Number   Major   Minor   RaidDevice State
0     0       8       17        0      active sync   /dev/sdb1
1     1       8       33        1      active sync   /dev/sdc1
2     2       8       49        2      active sync   /dev/sdd1
3     3       8       65        3      active sync   /dev/sde1
4     4       8       81        4      active sync   /dev/sdf1
5     5       8       97        5      active sync   /dev/sdg1
6     6       8      113        6      active sync   /dev/sdh1
7     7       8      129        7      active sync   /dev/sdi1

I was also able to activate /ded/md0 by running:

mdadm --assemble /dev/md0 /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1 /dev/sdf1 /dev/sdg1 /dev/sdh1 /dev/sdi1

...returning:

mdadm: /dev/md0 has been started with 8 drives.

+ NOW FOR THE PROBLEM: +

While the array appears to have restarted successfully, I don't see my 14TB partition which I have created 2 years ago (and used ever since to store all of my data). Running cfdisk shows only a single Linux partition with ~1.8TB of capacity and ~12TB of unused space:

Disk Drive: /dev/md0
Size: 14002195070976 bytes, 14002.1 GB
Heads: 2   Sectors per Track: 4   Cylinders: 3418504656

Name     Flags  Part Type   FS Type     [Label]     Size (MB)
--------------------------------------------------------------------------
                Pri/Log     Free Space              0.06                  
md0p1           Primary     Linux                   1750274.33
                Pri/Log     Free Space              12251920.69

The same also appears when running mdadm --detail /dev/md0

/dev/md0:
Version : 0.90    
Creation Time : Wed Jan  5 16:47:34 2011
Raid Level : raid5
Array Size : 13674018624 (13040.56 GiB 14002.20 GB)
Used Dev Size : 1953431232 (1862.94 GiB 2000.31 GB)
Raid Devices : 8
Total Devices : 8
Preferred Minor : 0
Persistence : Superblock is persistent

Update Time : Wed Oct 16 11:07:25 2013
State : clean 
Active Devices : 8
Working Devices : 8
Failed Devices : 0
Spare Devices : 0

Layout : left-symmetric
Chunk Size : 64K

UUID : e667bd7d:d55be409:e9e4094c:aa5ad989 (local to host wega)
Events : 0.1010

Number   Major   Minor   RaidDevice State
0       8       17        0      active sync   /dev/sdb1
1       8       33        1      active sync   /dev/sdc1
2       8       49        2      active sync   /dev/sdd1
3       8       65        3      active sync   /dev/sde1
4       8       81        4      active sync   /dev/sdf1
5       8       97        5      active sync   /dev/sdg1
6       8      113        6      active sync   /dev/sdh1
7       8      129        7      active sync   /dev/sdi1

If I understand correctly - the difference between "Array Size" and "Used Device Size" (2TB vs 14TB) means that there is a problem. I do not want to try to mount the partition until I understand what is going on (to avoid any changes to the data which would inhibit be from getting again access to my RAID group).

Any advice would be very much appreciated as I have been using this NAS server for all backups and digital media.

Did I forget to flip one last switch or am I totally screwed?

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1 Answer

Used Device Size means each individual disk is 2 TB. Don't use cfdisk as it is an old buggy POS that only understands the msdos partition table, which doesn't support disks > 2TB. Use parted instead, which supports gpt.

More importantly, I don't think you even have a partition table in the raid array. It is more typical to just format the whole array rather than partition it up, so just try mounting the array.

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