One original WD20EFRX in my Mirror (or Mirror 2 as I can’t see how to find the difference) died. After searching a bunch on here it came back after running a test and rebooting but I was thinking of still getting a spare just in case. The “P’ version is more available than the original & a higher spec but will it work if i replace one drive & leave the other original one. If not would the system work if I put two of those drives (or larger ones) in. Assuming I’d have to find a way of getting boot up software on to them for that.
1 - Regarding the drives:
Short answer: Do NOT buy WDEFRX drives. WDEFPX is a suitable replacement.
The WDEFRX, last I checked, are now SMR (Shingled) drives. I personally do not consider SMR drives to be a suitable for any purpose. Absolutely not in a NAS application. I stopped buying External 2.5” HDD’s because they now all use SMR drives.
Several years ago, there was a huge controversy when WD snuck SMR tech into the WD Red lineup without disclosing it. After the news broke, WD was forced to branch the WD Red lineup into the WD Red Pro, Red Plus, and Red product lines to mitigate the user base backlash.
Regardless of the brand: Verify the drives you buy are CMR and NOT SMR. If it’s not explicit: assume it’s SMR and avoid.
2 - How to upgrade
If your Mirror is set for Raid 1, you theoretically can just plop in the new drive, and the unit (with a few prompts) will copy over all the data on it’s own.
Theoretically, if you drop in a larger drive, and let the system restore, you will still wind up with a 2TB Raid array. If you then replaced your second larger drive - the mirror would repeat the process and you would still wind up with a 2TB array - - with larger drives.
HOWEVER. . .after the second drive is installed, it would be possible to run an “Expand” command to claim all available space on the drives.
3 - word of caution:
The mirrors are old devices. Your remaining drive is old. Doing a RAID restore within the unit is very drive intensive process. Lord help you if these actions trigger a “reindexing” event. (the cloud mirrors really don’t have the horsepower to efficiently reindex in the OS/5 world).
Before you do anything. . . backup the remaining drive to another device. Copying the data to an external SSD is much less stress than a RAID restore.
Thank you very much for this information. WD own website list the 3tb Pro drive cheaper than the 2tb. Cache is 256 compared to 64 for 2tb,would that be an issue if I managed to do a swap using the RAID?
I took a look at the WD website.
I am amused that the “red” (the straight “Red”, not the newer “red plus” and “Red Pro” lines) appears to be no longer offered. Good riddance. That takes the CMR/SMR issue off the table.
What I am seeing is from the WD website, Sept 6, 2025 is:
2TB Plus: 64mb, $79 ← long lead time
3TB plus: 256mb, $89
4TB plus: 256mb, $99
2TB Pro, 64mb, $99
3TB Pro, not listed
4tb Pro, 256mb cache, $139
The basic difference between Pro and Plus is the spinning speed, 5400rpm vs 7200rpm. That will affect theoretical transfer rate. To be honest, that’s probably not what’s controlling transfer speed overall and is irrelevant. The Mirror itself is probably a big constraint, and if you are connected over wifi to your PC. . .that’s probably the biggest constraint.
Any of these drives should work. The 4TB plus seems to be most cost effective. Bear in mind. . .the BOX itself is old. I would seriously consider a box upgrade with fresh drives.
Replacement is possible, but firmware compatibility and RAID synchronization support must be verified. It is recommended to back up data before replacement and ensure the new and old hard drives have identical capacity and rotational speed.
