I've recently started having some trouble with a pair of external hard drives. They're used exclusively for back up and I'm fairly certain all of their contents are available elsewhere, so I'm not terribly concerned about the data they contain. I would, however, appreciate some insight into what has happened, how it happened and/or what I might do to fix it.
The two hard drives were both formatted with a single ext4 partition. Within the last couple weeks, Arch Linux started to incorrectly detect them both as HPFS/NTFS/exFAT. Mounting them as I had been (with just -o rw), ownership/permissions do act as if the partition is ntfs. Using chown to change ownership would affect all directories but did not affect any files. If I use -o uid=myusername,umask=177,dmask=077 (which I'm pretty sure is all that's been necessary in the past to read and write ntfs partitions), I can then access files as well, but I still can not write anything new to disk.
After a bit of searching, I found a pair similar threads suggesting that fdisk/cfisk should be used to change the partition type back to 83. I used cfdisk to do so and both cfdisk and fdisk -l now show partition type as linux. Mounting with just -o rw and using chown does now change ownership of files as well, but it still does not allow me to write to the disk and ownership/permissions are not kept after unmounting/remounting. I'm not really sure where to go from here.
As to the potential source of the problem, the main point that comes to mind is that I booted into Windows 7 for the first time in at least a few months around that time. I don't generally leave these external hard drives connected except for when backing up, but it's possible that they were connected while booting Windows at one point. If they were connected, I definitely did not do anything that should have affected them, but I'm wondering if it's possible that Windows automatically did.
I highly doubt Windows itself would have done anything without your consent. For programs running in Windows, there's no telling, but if you don't have the security stuff turned off you should still have been prompted. Also, the fs type really shouldn't have any effect in Linux unless you're using a poorly written helper.
Anyway, give us something concrete to work with, s/a output of fdisk -l, lsblk -f, dumpe2fs -h, the relevant output of mount when the partitions are mounted, the permissions of the mountpoint when mounted, an example of the contents of the fs, etc.
Other thoughts: Have the partitions been fsck'd lately? Have you looked at your journal from around the time things started going sideways?
But whether the Constitution really be one thing, or another, this much is certain - that it has either authorized such a government as we have had, or has been powerless to prevent it. In either case, it is unfit to exist.