Support for WD Advanced Format disks
des at des.no
Tue Aug 10 17:44:50 UTC 2010
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
- Advanced Format disks should have a label that clearly describes them
- 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
% ./phybs -w /dev/adN
- 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
- 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.
Dag-Erling Smørgrav - des at des.no
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