xraid question

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exibar wrote:

so, silly to me question.  I'm picking up a Pro 6 RND6000-200 tomorrow.  I will flash the FW with 6.10.7 and then transfer my existing 4 x 4TB drives from my 214 over to it.  Currenlty running 6.10.7 as well as xraid.

 

  So if I have a spare 2 8TB drives over here, which I do, can I add those two drives into the array and have it expand the capacity of the volume by 16TB?  I know there is an order to do this, I have the KB bookmarked, I'm just asking at a high level.  I'm not used to being able to use different sized drives in a RAID array and actually use the full capacity of the larger drives.

  Traditional RAID, all 6 drives would have to be the same size, any that are larger you lose the additional space.  but XRAID is different I seem to be reading, correct?

 

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XRAID does support unequal size drives - 4x4TB + 2x8TB will give you a 24 TB (~18.18 TiB) volume with single redundancy.

The way this works:  The system will create a first RAID group that is 6x4TB RAID-5 (20 TB).  It will then create a second RAID group that is 2x4TB (4 TB) using the remaining space on the 8 TB disks.  These are concatenated into a single 24 TB volume.

If later on you replace upgrade a 4 TB drive to 8 TB, the second RAID group is converted to 3x4TB RAID-5.

The general capacity rule is "sum the drives and subtract the largest".  One limitation is that replacement drives need to be at least the same size as the one they replace.  If they are larger, there will be some space wasted unless they match the size of disks that are (or previously were) in the array.

For instance,

1. if you started with 6x4 TB
2. upgraded two disks to 6 TB (4x4TB + 2x6TB)
3. then upgraded them again to 8 TB (4x4TB + 2x8TB)

Then you could replace a 4 TB disk with either a 6 TB or 8 TB disk, and not waste any space.

But if you went directly from 6x4TB to 4x4TB + 2x8TB, then the volume wouldn't expand if you replaced a 4 TB disk with a 6 TB one.