misc/65494: dd bs size _MUST_ be N*512 - bug or feature

[Sheshka Alexey]

>Number:         65494
>Category:       misc
>Synopsis:       dd bs size _MUST_ be N*512 - bug or feature
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Apr 13 09:10:20 PDT 2004
>Closed-Date:
>Last-Modified:
>Originator:     Sheshka Alexey
>Release:        5.2.1
>Organization:
>Environment:
FreeBSD service.extmedia.com 5.2.1-RELEASE-p4 FreeBSD 5.2.1-RELEASE-p4 #0: Mon Apr  5 04:54:55 EEST 2004     root at service.extmedia.com:/usr/obj/usr/src/sys/SERVICE  i386
>Description:
While I'm making 
root at service.extmedia.com [~] # dd if=/dev/ad0 of=/dev/null bs=1000 count=10
dd: /dev/ad0: Invalid argument
0+0 records in
0+0 records out
0 bytes transferred in 0.000544 secs (0 bytes/sec)
it produse error, but
root at service.extmedia.com [~] # dd if=/dev/ad0 of=/dev/null bs=4096 count=10
10+0 records in
10+0 records out
40960 bytes transferred in 0.013014 secs (3147361 bytes/sec)
all good.

On OpenBSD and Linux all woks fine with _ANY_ value of bs ... Is it bug or feature in FreeBSD ?
If it is feature , I think this information must presents on it.
>How-To-Repeat:
      dd if=/dev/ad0 of=/dev/null bs=1000 count=10
>Fix:
      
>Release-Note:
>Audit-Trail:
>Unformatted: