[TriLUG] gpt problems

[Joseph Mack NA3T]

I've never done anything with a gpt partitioned disk before. I read up on it, 
got the latest gdisk and other fstools and have an EFI capable kernel. It didn't 
seem to be all that complicated. I bought a 4TB disk and put it in an external 
enclosure connected via a SATA cable.

I ran badblocks, put multiple partitions on the 4TB disk, formatted the 
partitions and wrote and read about 2.5TB just fine. No problems here.

I then moved the disk to an external USB enclosure, which is supposed to talk to 
4TB disks. gdisk sees all the partitions, but reports that the backup partition 
table is corrupt, while the main partition table is OK. I didn't try mounting 
any of the partitions.

I then moved the 4TB disk to a couple of other external USB enclosures, of 
indeterminate age (some are a year old, some may be 5yrs old), all of which work 
with 2TB disks just fine. All of them allow me to detect a 4TB disk with gdisk, 
but I get a range of results for the partitioning from detecting only one 
partition - the whole disk is a single protective mbr partition - to the disk 
appaering to be unpartitioned (as seen with the appearance of new devices in 
/dev/sd* and by gdisk).

Any idea what's going on here? I take it I have to be careful moving a 4TB disk 
between external enclosures, even ones that seem to be 4TB OK. I would expect if 
the enclosure detects the disk correctly (as 4TB) that the enclosure is just 
exporting blocks. From there the OS interprets the blocks via the partitioning 
and the filesystem. I must be wrong.

I wonder why the SATA connected enclosure and the supposedly 4TB capable USB 
enclosure see the 4TB disk differently (the USB enclosure sees a corrupt backup 
gpt table). Should I have done the partitioning in the USB connected enclosure? 
If so, on moving the disk to the SATA connected enclosure, would it detect the 
4TB partitioning correctly?

Thanks Joe

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) austintek (dot) com - azimuthal equidistant
map generator at http://www.wm7d.net/azproj.shtml
Homepage http://www.austintek.com/ It's GNU/Linux!