Can I mix CMR and SMR drives in my NAS RAID and how long these drives live?

How long will my NAS live?

I am very concerned about the SMR/CMR dilemma that we are currently embroiled with. I have a Synology DS218+, 1 1/2 years in service, fitted with x2 4TB WD Red CMR drives. My stockist still has 4TB CMR drIves on offer. Should I buy two more CMR drives now to put on the shelf to allow for future drive failure? As far as I have been able to determine, SMR drives can’t replace CMR drives, so if one drive fails in a 2-drive CMR NAS it is the same as a 2 drive failure if only SMR drives of similar size are available as a replacement option.

In your experience, how long will a Synology DS218+ chassis live in casual home service?

In your experience, how long will a 4TB WD CMR drive live in casual home service?

In your opinion, should I purchase two more 4TB WD Red CMR drives for future-proofing my NAS for the next 10+ years?

This scenario is a good topic for a Youtube video.


It depends on the use case. Heavily used drive in office environment would last around 2 years. Same drives at home might last 5 years or more. But is like a lottery. It might happen tomorrow. Statistically it should last long. NAS itself, I have seen lasting 5-10 years.
If one drive fails, you still have a data safe. Even if you put in SMR drive instead of CMR, it will still work. We are doing tests to determine the side effects.
So far we know that rebuild time is longer then it was with CMR drives only , when mixed. It is not recommended to mix these drives, but adding a SMR drive in a degraded RAID is better then adding no drive at all. You can then either replace other drives with SMR type too and avoid mixing for long term.
SMR drives will work in RAID environments. Even if they were slightly slower, you would not notice a difference since your NAS speed is limited to 1GbE Ethernet you have in place anyway. So if drives perform at 160MB/s per drive, NAS can only output 100-120MB/s in total with single LAN port.

So if your RAID has not failed, then I would get a spare CMR drive and leave it on the shelf. These drive wont be available for long.
I hope this helps.


If you have existing RAID with old 2TB/3TB/4TB/6TB EFRX CMR drives and you need a replacement drive or you want to expand your RAID with an extra drive make sure you get a right drive. You may want to get a spare drive before these old EFRX drive are not available any more.

Here are the codes for old CMR drives:

WD20EFRX – 2TB  –  Amazon  Ebay

WD30EFRX – 3TB –  Amazon  Ebay

WD40EFRX – 4TB –  Amazon  Ebay

WD60EFRX -6TB –  Amazon  Ebay

You might still get them in some places, but not for long.

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