Western Digital WD20EARX 2 GB SATA 3 disk

The Western Digital WD20EARX 2 GB SATA 3 disk is low powered, quiet, and fast enough for a reference disk. There is a previous model, WD20EARS, with identical hardware except for the SATA interface being SATA II instead of SATA III.

The disk I tested reports itself as model WD20EARX-00PASB0 with firmware 51.0AB15. The capacity is 2.0 TeraBytes or 2,000,398,934,016 bytes.

Advanced format

The minimum write rate for this disk is randomly bad, a problem caused by the disk using the unadvanced Advanced Format system where 512 byte sectors are stored in 4096 byte sectors. Normal disks write data in an ancient format where the data is cut up into 512 byte sectors. You would have read elsewhere how in the 1980s I was advocating 1024 byte sectors but the industry did nothing. By the 1990s there were many people asking for larger sectors and the disk manufacturers should have jumped up to 4096 bytes. Now the computer industry is making a change only because they are forced to change but they are giving us temporary crud instead of a real advance.

Rotational speed

The disk rotational speed is a big factor in access times. The standard disk rotates at 7200 Rotations Per Minute. The Seagate low power green disks rotate at 5900 RPM. The Samsung low power green disks rotate at the slightly slower 5400 RPM.The Samsung 2 TB equivalent is the Samsung HD204UI. Western Digital refuse to display the rotational speed in their specifications and instead talk about some rubbish they call IntelliPower. When manufacturers do that, it means they are hiding a weak point. The Western Digital WD20EARX has a rotational speed of only 5400 RPM and they want to hide their inferior rotation speed, compared to Seagate, using marketing junk speak.

Noise

Low power slow disks are quieter. Samsung and Seagate compete for the quietest disks. Hitachi and Western Digital have some really noisy disks. The Western Digital WD20EARX is really quiet and almost as quiet as the Samsung equivalent.

Reliability

Everyone has their stories about which brand is reliable. I found in the past that Seagate was reliable and Western Digital was less reliable. In the 2 TB low power models, industry insiders report fewer returns for the Western Digital models. Offsetting that is that fact that Western Digital sells several very similar sounding disks with different internal mechanisms. The WD20EARX appears to have the most reliable internal design. Samsung also has a reliable equivalent. Hitachi disks should be reliable but they fail the noise test and I have not found anyone using Hitachi low power disks in large volumes.

Speed tests

The disk has a SATA III interface and is only fast enough for SATA II. The following tests show the disk can run close to the maximum speed of SATA I and nowhere near the maximum speed of SATA II. SATA III is nearly a waste on this disk and will provide extra speed only where you frequently re-read data that is in the disk 64 MB cache. If you use a good operating system, the data will already be cached in memory and not need a read from the disk cache.

SATA II test

The maximum read rate is bumped up by reads from cache. It should be around 110 MB/s. The minimum read rate should be half the maximum, or 55 MB/s, because that is the difference between the long outer tracks on the disk and the short inner tracks. The minimum read rate is 48 MB/s, instead of 55 MB/s, for some unknown reason.

The maximum write speed would be the same as the maximum read speed if the disk was not infected with the Advanced Format disease. The varying results depend on cache. The 57 MB/s write rate is the case where the data is not in cache and the disk has to read before writing. The 110 MB/s occurred on the second test because the required sectors were in the cache. The minimum write speed in test 1 is what you can plan on with normal use when the data is not in the disk cache. The 41 MB/s write speed from test 3 is what you might get if you are continually updating the same sectors and they are always in the cache.

USB 3

The USB 3 speeds are almost identical to the SATA II speeds because USB 3 is also faster than the disk. The faster write rates are the result of the disk cache filling up with the data needed for the sector updates. The USB 3 test would be closer to the SATA II test if i switched the machine off between tests.

USB 2

USB 2 has a maximum speed of 480 Megabits/second which is about 48 MegaBytes/second. About 10 percent or 5 MB/s is used for overheads giving a practical speed of 43 MB/s. The USB 2 test shows a consistent speed around 33 MB/s suggesting another 20 percent is lost in overheads for small reads and writes.

Test 4 is a test using USB 2 with another application running. USB 2 is so slow, compared to the disk speed, that you can run other applications without slowing down the disk activity.

Price

The Western Digital WD20EARX sells at the same price as the Samsung equivalent and slightly below the Seagate equivalent with the price difference less than the cost of petrol to drive across town to pick up the disk. The Samsung is slightly faster and is my choice when the price is the same. If the Western Digital disk was on sale locally at a significant discount and the Samsung was not, I would buy the Western Digital.

Conclusion

The Western Digital WD20EARX sells at the same price as the Samsung equivalent, is almost as fast, and is almost as quiet. I am happy with either disk for a backup disk or something on the end of a USB 2 cable. I would not use either when I want speed.