Xubuntu liveCD 11.04 running on bad machine with mdadm RAID1 array with an unrecognizable ext4 filesystem:To rescue some files, I installed a new hard drive and formatted it to ext4. I copied 300GB worth of files retrieved from bad machine data scraping onto the newly formatted ext4 drive. I powered down the machine and removed the HDD, connected HDD to an ubuntu good machine.Good machine doesn't recognize the ext4 filesystem. Trying to mount, dmesg reports:EXT3-fs (sdd1): error: can't find ext3 filesystem on dev sdd1.EXT4-fs (sdd1): VFS: Can't find ext4 filesystemEXT4-fs (sdd1): VFS: Can't find ext4 filesystemSo I put the drive back in the bad machine, and the filesystem is recognized and mountable.Experimenting, I formatted another new drive to ext4 on good machine, then installed the drive on bad machine. Bad machine doesn't recognize new drive formatted by good machine.What could cause bad machine to speak it's own ext4 language? Can the ext4 filesystem that bad machine is creating be corrected on good machine so the data can be copied onto good machine?Edit 0As requested by @bersh, command output on bad machine:# cat /proc/filesystemsnodev   sysfsnodev   rootfsnodev   bdevnodev   procnodev   cgroupnodev   cpusetnodev   tmpfsnodev   devtmpfsnodev   debugfsnodev   securityfsnodev   sockfsnodev   pipefsnodev   anon_inodefsnodev   devpts        ext3        ext2        ext4nodev   ramfsnodev   hugetlbfsnodev   ecryptfsnodev   fuse        fuseblknodev   fusectlnodev   pstorenodev   mqueue        btrfs        iso9660nodev   overlayfs        squashfsand the next one:# lsmod|grep ext#(no output)UPDATE 1I realized I have been doing something wrong... The raid array is partitioned, I've been assembling the entire /dev/sda disk with mdadm when I should be assembling individual partitions: mdadm -A /dev/sda1 /dev/md5 and mdadm -A /dev/sda2... That doesn't answer the question though. because the non-raid ext4 partition was unrecognized on the good machine, and even if I correctly assemble the raid array, I might not be able to transfer it to a different machine and the different machine be able to recognize the ext4. 
Why is my ext4 filesystem recognizable only on the machine it was formatted on?
filesystems;ext4;raid;mdadm