WD silently replace EFRX with EFZX drives(2-6TB)

WDxxEFZX silently replacing WDxxEFRX?

I am in the looking to replace my WD Red 3TB drives with WD Red Plus 6TB drives (making sure CMR tech is used). Now i noticed that a new WD Red Plus line has entered the market in 2021, namely the EFZX series with 128mb cache instead of 64mb cache currently used by the EFRX series.

If i search WD website for the plus series and end up on the URL below, it seems WD is working on silently replacing the EFRX line with the EFZX line (you can see this by expanding the “recording technology” paragraph on the page.. they only mention the 1 TB as EFRX, the rest is replaced).


Now for my question: EFZX is not listed yet on Synology website, the double cache size appeals to me naturally. Should i hold out for Synology to update the list, should i take a leap of faith due to this being a “Red” nas-specific drive, or should i play it safe and order EFRX drives instead and just be happy with 64mb cache?

These new drives seem to be an upgraded version of their older CMR drives that used the same recording technology. When they silently replaced CMR with SMR drives they had more cache available. Now they have matched the cache size with their SMR drives. In a RAID situation, you will not benefit from this cache since all data is written randomly across many drives. But it is interesting that their speed has been increased from around 150 to 170 MB/s. If you have older drives that are slower you will not benefit from this. But if you have a new NAS then certainly choosing these faster drives would theoretically improve NAS speeds. In the existing setup, the speed will be as fast as the slowest link in the chain. If you connect via 1GbE LAN then you will not notice a speed difference anyway.

If you are wondering if these drives are compatible with Synology then the answer is yes they are.

If you wonder if you can mix them with the older type of drives, the answer is yes you can.


WD101EFBX (10TB)
WD120EFBX (12TB)
WD140EFGX (14TB)


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9 thoughts on “WD silently replace EFRX with EFZX drives(2-6TB)

  1. I added a WD40EFZX 4TB drive to a raid controller RocketRaid 840A having a number of WD40EFRX drives already working in RAID5, and the rr3740A.sys driver stopped the OS (Win 11) with note IRQL_NOT_LESS_OR_EQUAL stop code. I will try to order/add a WD40EFRX drive, attach to the RR840A RAID controller, and see what happens. System boots and is stable with the EFZX drives attached to the MB (Asus Z390) Sata connectors.

  2. For those googling for the answer whether combining WDEFRX and WDEFZX (WD40EFRX and WD40EFZX in my case) would be safe.

    Had to replace one of broken/failing WD40EFRX with WD40EFZX in my Synology DS218j. So far (10 days) no problems at all. WD40EFZX is very quiet and 2°C-3°C cooler than WD40EFRX.

  3. HI! I have a Synology NAS with two WD40EFRX. One of them has errors and I want to replace it. A new WD40EFRX is out of stock nearly everywhere so the solution could be buy a WD40EFZX. Any problem for my NAS it it runs with one WD40EFRX and one WD40EFZX? THANK YOU VER MUCH IN ADVANCE

    1. I actually have a similar problem with a My Cloud EX2 Ultra NAS with drive 2 being (SMART) reported as in impending Fail state. The NAS has two WD40EFRX drives. Will mixxing it with a WD40EFZX drive be a safe solution? Thanks in advance for any feedback.

    2. Hi, I have exactly the same situation in my Netgear NAS with one failing WD40EFRX drive out of two. If you get any answer elsewhere it would be great if you could update here as well. Thanks a lot!

        1. Hi, some time after I posted my question here I went ahead and purchased a WD30EFZX and successfully swapped my failing WD30EFRX disk. I have not had any issues whatsoever. All working just fine. Just noticed in my original post that I wrote it was a WD40EFRX disk failing, but it was a WD30EFRX in my case but it shouldn’t make any difference, just different size.

  4. Thanks for writing up this article. Just the information I was looking for to replace my WD red plus drive on a synology