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Duplication users - how much free space do you have?


beatle
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I currently have 7 drives in my pool (3, 5, 8, 8, 8, 14, 14) and I have just shy of 12TB free.  My most full drive (a 14TB) has 8.26TB of data on it, so if it were to crash, the other drives would need to pick up the duplication slack, so I think I could be just a touch short if I lose a big drive.  Of course I wouldn't lose data, but I'd need another drive pronto to get out of hazcon state.

How full does everyone else let their pools get?

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First, if the Pool has 12TB free and one HDD has 8.3TB used, then you are not even able to endure the loss of a 14TB drive. The fullest drive has 5.7TB free and if that drive fails, you lose that 5.7TB as well. So then you'd have 6.3TB free on the other drives to cover for the 8.3TB on that 14TB HDD. That won't work. So if it fails slowly, such that Scanner may trigger an evacuation, but you don't add a HDD before it fails completely, you may lose data (assuming no backups).

I use duplication for resiliency/up-time and as such always ensure that any Pool has more free space than the largest HDD in that Pool.

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Right, as I mentioned I would be a touch short.  Though with everything duplicated I wouldn't lose data if a drive fails; I just wouldn't be able to automatically recover from hazcon state of having some of my data on only one drive.  I think of this like running RAID 5 without a hot spare.  If I lose a drive from a RAID 5 group, the data is still there and accessible by calculating the block using parity data, but the rebuild to full redundancy won't be able to occur automatically - a spare drive would have to be installed.  With Drivepool the data at risk before a full duplication would be whatever the remaining disks couldn't duplicate from the failed drive.

To save a few bucks on electricity I am leaning towards having a few cool spares in drive caddies that I could pop into the box while a full size spare is sourced.

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