ARGH! Root cause: 4k sector size while harddrives report 512byte sectors.
Misaligned partitions will cause severe performance penalties  and block
IO in the process - causing VDR to lose frames.
Thank you very much, WD, wasted a lot of time and money on this sillyness.
Re-aligning the partitions for the 4k boundaries fixes all performance
issues. Just a heads up to others who might have missed this detail.
 http://en.wikipedia.org/wiki/Advanced_Format#Advanced_Format_512e :
> The translation process is more complicated when writing data that is
> either not a multiple of 4K or not aligned to a 4K boundary. In these
> instances, the hard drive must read the entire 4,096-byte sector
> containing the targeted data into internal memory, integrate the new data
> into the previously existing data and then rewrite the entire 4,096-byte
> sector onto the disk media. This operation, known as read-modify-write
> (RMW), can require additional revolution of the magnetic disks, resulting
> in a perceptible performance impact to the system user.
vi...@tyldum.com PGP: 0x3110AA98
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