Support for WD Advanced Format disks

[Dag-Erling Smørgrav]

I'm looking into a clean, permanent solution for WD Green drives that
use 4096-byte physical sectors.  To summarize the information I've
collected so far:

 - There are several types of WD Green disks.  I am primarily interested
   in the 1+ TB models: EARS and EADS.

 - According to WD's own documentation, EARS disks are Advanced Format
   while EADS disks are not; furthermore, EARS disks have 64 MB cache
   while EADS disks have only 32 MB.

 - There is at least one source that provides model and serial numbers
   for two EADS disks that seem have the performance characteristics of
   an Advanced Format disk.  One of them actually reports 4096-byte
   sectors, the other does not.  I am not entirely certain that source
   is reliable.

 - Advanced Format disks should have a label that clearly describes them
   as such:

http://media.bestofmicro.com/U/O/238272/original/Western-Digital-WD10EARS-top.jpg

 - I received an EADS disk and performed measurements which clearly show
   that it is *not* an Advanced Format disk.  I had no trouble achieving
   50 MBps with misaligned 8192-byte writes.

Right now, I have two requests.  The first is that people who have
Advanced Format disks run a program I wrote that measures the
performance of aligned and misaligned writes of different sizes.

% svn co http://svn.freebsd.org/base/user/des/phybs
% cd phybs
% make
% ./phybs -w /dev/adN

Please note:

 - This test is *destructive*.  Do not run it on a disk that contains
   data you care about; it *will* destroy them.

 - You can not run it on a file, but you *can* run it on a partition
   instead of the whole disk.  You can even run it on a misaligned
   partition; the results will show by how much the partition is
   misaligned.

 - The test takes a long time.  It took about half an hour on a WD20EADS
   connected by eSATA.  It may take several hours on an Advanced Format
   disk.  If you are impatient, try bumping MINSIZE to 1024 in phybs.c.

The second request is for some kind soul to send me an EARS drive to
play with; please contact me off-list if you're interested.

DES
-- 
Dag-Erling Smørgrav - des at des.no