Same HDD Model differing capacity

I have two identical drives but they are reporting different sizes. The only difference I can see is fw revision [NE01 vs NE00]. TrueNAS warns me that these are not the same size, is this going to be a problem when creating raidz2?


  • 8 identical (by model number) drives 1/2 show 11.7 TB all the rest show 12.0 TB (smartctl).
  • formatted all drives using following command:
    sg_format --format --fmtpinfo=0 /dev/da[2-9]
  • Version: TrueNAS-13.0-U6.1

I have absolutely no idea why they would be of differing capacities. Tried a quick search for the model number and “11.7” and found no matches.

TrueNAS will complain but if I remember correctly it will go through, and ZFS will only use the capacity of the smallest disk.
In effect it should treat all the disks as if they are 11.7T.

My guess is who manufactured it? was it WD or Hitachi? check manufactured date that might help?

Different revision numbers on the drives. NE01 vs NE02. My guess is that they are indeed different in amounts of space. Could confirm on second system to sanity check that it isn’t a truenas quirk. If it was SSDs instead of HDDs I’d wonder if they increased reserve space to increase TBW, but since it is HDDs I have no clue why there’s be a difference other than different components for cost savings.

Edit// wouldn’t be a problem, as essinghigh stated it’d just be a touch of wasted space & pool will be treated as if everything was 11.7TB

Be sure you restart after changing block size with sg_format like that, if you haven’t already.
Sometimes outdated data about the available capacity can linger until you do.

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