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 filesystem EXT4-fs (sdd1): VFS: Can't find ext4 filesystem
So 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?
As requested by @bersh, command output on "bad machine":
# cat /proc/filesystems nodev sysfs nodev rootfs nodev bdev nodev proc nodev cgroup nodev cpuset nodev tmpfs nodev devtmpfs nodev debugfs nodev securityfs nodev sockfs nodev pipefs nodev anon_inodefs nodev devpts ext3 ext2 ext4 nodev ramfs nodev hugetlbfs nodev ecryptfs nodev fuse fuseblk nodev fusectl nodev pstore nodev mqueue btrfs iso9660 nodev overlayfs squashfs
and the next one:
# lsmod|grep ext #
I 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.