Try to "self-test" the disk with the "Disks" utility in the "System settings"
(the corresponding entry is to be found in under the menu button in the
upper-right corner of the interface). It looks like the disk is not OK and
you do not want to use a disk that may fail at any time.
Also, why ext3? Maturity is not a goos answer: in the latest 4.3 version of
the kernel, ext3 is handled by ext4's code. Ted T'so gave in
http://lkml.iu.edu/hypermail/linux/kernel/1508.3/05063.html the rationale for
the removal of ext3 as a separate filesystem:
The main rationale is that two code bases is harder to support than
one. When bugs get fixed in ext4, they don't necessarily get
back-propagated to ext3 except for a manual process where Jan notices
that a bug fixed in ext4 is also in ext3, and he manually ports the
patch over.
Both Red Hat and SuSE, as well as Debian and Ubuntu, are using ext4
with CONFIG_EXT4_USE_FOR_EXT23 for a couple of years now to support
ext2 and ext3 file systems. So with the exception of some really
ancient enterprise Linux distros, and people who are manually
configuring their systems, very few people are likely using ext3 code
base, which means the chances that it bitrots increases. Basically,
it's only been Jan's tireless work that has kept that from happening,
given that all of the major distro's have been using ext4 to support
ext2 and ext3 file systems.
