Do someone know were I can find the tech spec for HDD reference WD30NMZW-11GX6S1 that is inside WD Elements 3TB / WDBU6Y0030BBK ? size of cache (I saw 128MB somewhere) but I want to know if there is some other kind of secondary cache ? is this drive a hybrid SSD+HDD ?
The internal drive inside your external hard drive may vary depending on application. Depending on model, the internal hard drive in an external enclosure could be either SATA or native USB.
We don’t know a particular internal hard drive model, data interface, rotational speed, or cache size in the external hard drive enclosure. Dismantling any single-drive external enclosure to obtain this information will void the warranty of the hard drive.
It’s definitely not a “Hybrid” HDD … if it was, they would advertise it and it would also be reflected in the price. (which would be higher)
And the cache would definitely not be 128MB. And be aware that the cache size makes no difference in performance of an external hard drive. Data rate transfer is bottlenecked at the USB transfer speed.
The quote you copied say no performance but you forgot the note below it “With the exception of Thunderbolt, eSATA and USB 3.0 external hard drives” because the WD Elements I have is USB 3.0 and connected to USB 3.0 port so yes cache have performances effect.
Plus whenever it is only USB 2.0 it could still have some performance effect when there are a lot of head activity (seek-time) if this activity make the hard drive slower than USB 2.0 max speed (if re-read data are still in cache that mean less seek-time loss).
And the reason why I am asking all this is because this hard drive provide strange benchmarks result compared to all other mechanical non-Hybrid hard drives I have (internal or external).
For example it can provide a stable reading curve all over the disk surface that “should” not be possible with mechanical hard drives because the closer you go to inner side of the disk surface the less data you read per rotation, this HDD also provide very good results (ten times higher than usual) on CrystalDiskMark with 4K block write test.
So I am trying to find an explanation and figure out how this is possible or if this drive fools the benchmark tools (and id it does … how ?).
Hope my english is not too bad, I am not english native.
WD are now using SMR (Shingled Magnetic Recording) instead of PMR (Perpendicular Magnetic Recording) on their external hdd’s. Which is most probably why you’re seeing strange benchmark results because data is handled a different way.
I know for a fact that my 4TB My Passport Ultra which is a few years old is 100% an SMR Hard Drive.
The main info in this article is for me “huge disadvantage new data must be re-sorted and rewritten, so that data rates fall sharply … hard drives using this technology are suitable as archive drives that are rarely written but often read,”
The purpose of this disk will be to store data as archive so it’s OK for me.
But if this slight tracks overlap trick permit to get +25% space I do not understand how this disk can provide such linear readind speed curve all over the disk surface and can write 4K block 10x faster than usual.
edit : I found a very interesting review about a Seagate SMR based HDD that explain the high performance writting 4K blocks because of big memory cache capacity of the HDD (bench showed with the Seagate show same very good 4K writing result and access time.
This is why I still think the WD Element use a big memory cache size and this 128MB may not be “impossible”.
Yes I understood the “impossible” that way too, but it was the easiest way to explain the performances, and since then I’ve been digging Pros-Cons about SMR technology and found also other testers that also found 4K writings to be 10x faster on other SMR based HDD like Seagate and those drives carry 128MB cache memory.
Anyway I am glad I learned about this SMR technology I wasn’t aware of.
But after reading the Pros/Cons about SMR I am estonished that constructors do not clearly indicate the use of SMR on the coverboxes, I think people should be informed and make a choice depending the usage they plan to have for the HDD.
I have a similar experience to Dodfr, but instead it is about two WDBU6Y0040BBK-0A (WD Elements 4TB) that I had the opportunity to benchmark.
The disks inside are the exact same model (WD40NMZW-11GX6S1) and the exact same firmware too. The difference is on the outside - one is the 2016 model with white painted logo and the other is the 2017 model with engraved logo. I am not sure that they are exact 2016 and 2017 models, but I have seen that is what they are called.
Both tests gave completely different test results.
For the 2016 model I got normal(?) write speeds of 70-110 MB/s all through the test. For the 2017 model I got normal write speeds until I hit 25%, then it dropped to 0-50 MB/s. Then I thought I understood the case - the 2016 model was PMR and the 2017 was SMR. But that was before I benchmarked in HD Tune.
The 2016 model has a very SMR like curve to me, even if the average and minimum speeds looks PMR at 80 to 105 MB/s.
But this is nothing compared to the 2017 model, which clearly is an SMR even in this case with a straight graph and speeds of 220 MB/s.
I have tested a 2 TB WD Elements and it has a normal graph that falls down the closer it gets to 100%.
I can conclude that anything above 2 TB is not PMR and that the 2017 model is SMR. It acts like an SMR disk - when the unknown cache is exhausted, then it gets very slow.
But I am not sure what the 2016 model is - it did not show any speed drops with fio but it still has an SMR graph.