[TriLUG] 512/4096B cluster size incompatibilities

[Joseph Mack NA3T via TriLUG]

I've just found that the logical cluster size matters to the user. I assumed 
this was a hardware layer problem sufficiently deep that it would not directly 
affect me.

I have two identical model Seagate 4TB drives, bought the same day, from Intrex
(this was a while ago)

Model Family:     Seagate Desktop HDD.15
Device Model:     ST4000DM000-1F2168

Both have been functioning perfectly (as data disks) since I bought them.

To avoid any tom-foolery from the manufacturer, I have been buying the same 
submodel disks (M000) from Amazon, ever since, even though I'm not buying the 
current submodel anymore.

As I found out this morning, despite the same model and submodel numbers, the 
two disks aren't identical. One has a 512B logical cluster size and the other 
has a 4096B logical cluster size.

I wanted to copy one disk to another. I had a bunch of external drive 
enclosures. I dd'ed from the source disk (4096B cluster) to the target disk 
(512B cluster), without any errors from dd. However the target disk had a crazy 
single partition, which wouldn't mount. I confirmed that I could write to the 
target disk by erasing its partition table (copying /dev/zero to the beginning 
of the disk).

The same thing (no errors) happened using ddrescue resulting in the same crazy 
partition table.

Thinking the problem was the drive enclosure for the target disk (new and 
supposed to work with 8TB disks), I got out an old enclosure that was known to 
work with 4TB disks and used it on the target disk, again with the same result 
(ddrescue, no errors).

I concluded there was something about the target disk and not the enclosure. 
Rather than dd'ing from the source disk, I partitioned the target disk to have 
the same sized partitions as the source disk (so I could copy files into the 
partitions). I noticed that the sector numbering was quite different. Then I 
noticed that the logical sector sizes were different.

I also noticed that the 512B 4TB disk wasn't recognised by one of my external 
enclosures (not seen in /dev/sd* while the LED on the front of the enclosure 
flashed rapidly), while the 4096B 4TB disk was recognised.

I take it you can't dd or ddrescue between disks of different cluster sizes and 
if you do, you won't get error messages.

I also take it that external enclosures for 4TB disks need to have the right 
cluster size for the disk, in order for the disk to be recognised.

Joe

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