[TriLUG] How to identify a block device's filesystem type?

[Michael Coburn]

Hi,

I have some hard drives laying around, that were once part of a mdadm RAID5
array.  I put them back together using --assemble, but I can't remember
what filesystem I had formatted them with.  Does anyone know how I can
sample the block device and know conclusively what filesystem is on there?

It won't mount:

root at raspbx:~# mount /dev/md0 /media/data/
mount: wrong fs type, bad option, bad superblock on /dev/md0,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

root at raspbx:~# fdisk -l /dev/md0

Disk /dev/md0: 1000.2 GB, 1000215543808 bytes
2 heads, 4 sectors/track, 244193248 cylinders, total 1953545984 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 65536 bytes / 131072 bytes
Disk identifier: 0x00000000

Disk /dev/md0 doesn't contain a valid partition table

root at raspbx:~# mdadm --detail /dev/md0
/dev/md0:
        Version : 0.90
  Creation Time : Sat Oct 11 19:39:57 2008
     Raid Level : raid5
     Array Size : 976772992 (931.52 GiB 1000.22 GB)
  Used Dev Size : 488386496 (465.76 GiB 500.11 GB)
   Raid Devices : 3
  Total Devices : 2
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Thu Oct 24 13:42:14 2013
          State : clean, degraded
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 64K

           UUID : ec499738:2185dff1:766caf6a:1af60f76
         Events : 0.115446

    Number   Major   Minor   RaidDevice State
       0       0        0        0      removed
       1       8       16        1      active sync   /dev/sdb
       2       8        0        2      active sync   /dev/sda

I have them connected to a raspberry pi running raspbx - Asterisk (Debian
based)
root at raspbx:~# cat /etc/*release
PRETTY_NAME="Debian GNU/Linux wheezy/sid"
NAME="Debian GNU/Linux"
ID=debian
ANSI_COLOR="1;31

dmesg:
[7611406.513739] scsi 18:0:0:0: Direct-Access     ST350032 0AS
      PQ: 0 ANSI: 4
[7611406.532182] sd 18:0:0:0: [sdb] 976773168 512-byte logical blocks: (500
GB/465 GiB)
[7611406.569174] sd 18:0:0:0: [sdb] Write Protect is off
[7611406.583465] sd 18:0:0:0: [sdb] Mode Sense: 38 00 00 00
[7611406.590171] sd 18:0:0:0: [sdb] No Caching mode page present
[7611406.599980] sd 18:0:0:0: [sdb] Assuming drive cache: write through
[7611406.627998] sd 18:0:0:0: [sdb] No Caching mode page present
[7611406.637617] sd 18:0:0:0: [sdb] Assuming drive cache: write through
[7611406.675618]  sdb: unknown partition table
[7611406.704149] sd 18:0:0:0: [sdb] No Caching mode page present
[7611406.713733] sd 18:0:0:0: [sdb] Assuming drive cache: write through
[7611406.723827] sd 18:0:0:0: [sdb] Attached SCSI disk
[7611440.826363] md: md0 stopped.
[7611440.865723] md: bind<sda>
[7611440.881015] md: bind<sdb>
[7611440.915728] bio: create slab <bio-1> at 1
[7611440.925684] md/raid:md0: device sdb operational as raid disk 1
[7611440.936370] md/raid:md0: device sda operational as raid disk 2
[7611440.952322] md/raid:md0: allocated 3176kB
[7611440.970557] md/raid:md0: raid level 5 active with 2 out of 3 devices,
algorithm 2
[7611440.995994] RAID conf printout:
[7611440.996026]  --- level:5 rd:3 wd:2
[7611440.996043]  disk 1, o:1, dev:sdb
[7611440.996055]  disk 2, o:1, dev:sda
[7611440.996300] md0: detected capacity change from 0 to 1000215543808
[7611441.082733]  md0: unknown partition table
--
michael