fdisk reports a wrong disk size on a faulty disk
While trying to backup a faulty disk before attempting recovery, I find that its size is reported wrong. What can it mean?
My disk is supposed to be 3.0TB (~2.73 TiB), containing one single NTFS partition (and whatever windows adds when you ask for a single big partition)
dmesg reports (after USB insertion of the faulty disk):
[ 6802.040821] sd 14:0:0:0: Attached scsi generic sg4 type 0
[ 6802.040997] sd 14:0:0:0: [sde] 1565565872 512-byte logical blocks: (802 GB/747 GiB)
[ 6802.041467] sd 14:0:0:0: [sde] Write Protect is off
[ 6802.041473] sd 14:0:0:0: [sde] Mode Sense: 00 38 00 00while fdisk -l reports
Disk /dev/sde: 746.5 GiB, 801569726464 bytes, 1565565872 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: BA3C953A-7F37-4DBA-864A-9B551DB94B48
Device Start End Sectors Size Type
/dev/sde1 34 262177 262144 128M Microsoft reserved
/dev/sde2 264192 5860530175 5860265984 2.7T Microsoft basic dataClearly showing a partition bigger than the disk itself, which puzzles gparted
Also, mount --read-only -t ntfs /dev/sde1 fails with NTFS signature is missing
Question: what does it mean? Simply that something is wrong in the GPT? A hardware failure on 2/3 of the physical storage (like inaccessible surfaces/read heads)?
Side notes:
- the failure occurred with a crash of windows
chkdsk - the disk is a 3.5" HDD hosted in an external USB case (externally powered)
1 Answer
In all probability, this is the source of your problem:
the disk is a 3.5" HDD hosted in an external USB case (externally powered)
External USB enclosures often impose 32-bit limitations on disk sector values. 2^32 sectors, times a 512-byte sector size, means that these enclosures can handle, at most, 2 TiB disks. Frequently, the symptom of using a disk bigger than this is that the disk size is reported as the disk's true size modulo 2 TiB -- that is, your 2.73 TiB disk is reported as 0.73 TiB. This is akin to an older car's odometer "rolling over" -- a car with a 5-digit odometer and 127,000 miles would show a value of "27,000 miles," since there's no sixth digit for the "1." Of course, new cars all support six digits in their odometers, just as newer disk interface methods (like SATA) support more than 32-bit sector addresses -- but most (maybe all) USB enclosures support just 32-bit sector addresses.
There are three solutions to your problem:
- Use the disk internally, or as an eSATA (external SATA) disk. This will enable you to use its existing partition table and any data that was stored on the disk when it was partitioned and used internally to begin with. In theory, a USB enclosure that supports 64-bit sector addresses would work, too, but I don't know of any such enclosure.
- Get a new USB enclosure that translates blocks of eight 512-byte sectors into individual 4096-byte sectors. This raises the limit from 2 TiB to 16 TiB. The problem is that your current partition table will be rendered invalid, so you'll need to back up any data from an internal connection, then put the disk in the new enclosure, then re-partition the disk and restore the data. (It's sometimes possible to muck with the partition table to avoid the backup-and-restore procedure, but doing so requires expertise that I suspect you lack, so I don't recommend you try it. Depending on the exact partition layout, it also might not be possible at all.)
- Use just a fraction of the disk's capacity. You'll need to back up your data and create a fresh partition table that gives you access to just some of the disk. Obviously, this is not a good long-term solution, but it might be adequate in the short term if you desperately need to use the disk now but don't need its full capacity right away.
