It looks like one of my hard drives failed in our RAID 6 (4 x 2TB) configuration. Unfortunately, I only have immediate access to a 1TB drive. Would there be an issue with temporarily replacing the 2TB with a 1TB drive?

At this time, we are consuming 1.95TB of data our of a possible 4 TB.

I also do realize that I do have up to 2 drive failures before the array fails, I'm being paranoid.

  • Yes there would be a problem, in that it can't be done AFAIK. You can replace a failed disk with a larger disk but not with a smaller disk.
    – joeqwerty
    Sep 30, 2014 at 22:36

1 Answer 1


In short, yes... you would have a problem with RAID6 and using a smaller drive. RAID6 itself has no way to dynamically re-size the RAID to a smaller disk. You must either:

  1. have a RAID controller capable of dynamically resizing the RAID volume
  2. copy your data elsewhere, and completely rebuild the RAID and then restore the data back to the volume.

I have only ever seen one RAID card that could do dynamic resizing, but it did not support RAID6. I doubt yours would either. Also, even with RAID5... there was a HUGE hit on performance while the raid was resizing.

Copying your data elsewhere is also a big risk, due to the fact that you're taking your redundant array... and moving the data to a non-redundant storage. (even if it is temporary)

At the end of the day... just buy another 2tb hard drive. They're not terribly expensive... and trying to avoid it will just give you much higher risk of data-loss.

In the future... you might want to look at other RAID alternatives that do support that sort of functionality. ZFS can... as well as a few other proprietary RAID appliances (DroboFS, etc...) allow you to use mis-matched drives for redundancy. I honestly would not recommend anything but ZFS for this sort of thing.

  • ZFS does not support dynamic resizing. You can increase the size of an existing vdev by replacing disks one at a time with larger disks and rebuilding (resilvering) the array between each disk replacement. Other than that you have to expand the zpool by adding another vdev or rebuilding it from scratch. Appliances made by companies like Drobo and Synology do support dynamic resizing.
    – Gene
    Sep 30, 2014 at 23:55
  • @Gene Thanks for that. My depth of knowledge with ZFS is somewhat limited. I thought I read somewhere that it did support dynamic resizing and automatic 'resilvering'. Good to know.
    – TheCompWiz
    Oct 1, 2014 at 18:06

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