I was writing to /dev/null.  It doesn't seem to have an issue.

This appears to be related to "iflag=direct" more than anything.

W/o direct it works, but, for example I can't use iflag=direct with 
/dev/zero
for even a 4K block size.

Hmmm....




Paul Eggert wrote:
> On 10/12/2012 02:14 AM, Pádraig Brady wrote:
>   
>> if you specify ibs and obs seperately,
>> then you will get writes of the size you requested at least.
>>     
>
> Won't there be similar problems with the write system
> call too?  Perhaps not on Linda's system, but on other
> systems.  Once the buffer size exceeds 2 GB or so,
> things get pretty dicey in the wild, not due to any
> problem in dd itself, but due to the kernels or
> file systems that dd relies on.
>