Greater than 80% volume capacity: OK for large static storage?

[Robert Trevellyan]

Yet even though my eight drives are identical sizes, and listed together next to a single plus button, the GUI splits them into two (vdevs?) of four drives each.

I see your point, but there's a difference between grouping same-size drives into vdevs and dividing same-size drives between vdevs. Generally speaking, a pool of two 4-drive vdevs would give you higher IOPS than one 8-drive vdev, at the expense of capacity. Whether you like the default really depends on how you choose to define "optimal". The person who developed the heuristics in that dialog had to make a pragmatic decision. Performance, capacity and reliability are orthogonal when it comes to optimization.

 

[RedBear]

I see your point, but there's a difference between grouping same-size drives into vdevs and dividing same-size drives between vdevs. Generally speaking, a pool of two 4-drive vdevs would give you higher IOPS than one 8-drive vdev, at the expense of capacity. Whether you like the default really depends on how you choose to define "optimal". The person who developed the heuristics in that dialog had to make a pragmatic decision. Performance, capacity and reliability are orthogonal when it comes to optimization.

I get what you're saying. So it decided for me that I wanted more performance in exchange for less capacity. Seems like the proper way to do a heuristic in this case would be to at least ask the user to decide which of the three orthogonal aspects are more important for the pool they're trying to create. Then the algorithm would have a much higher chance of automatically creating a pool structure that actually corresponds to what the user wants/needs.

 

[Robert Trevellyan]

Seems like the proper way to do a heuristic in this case would be to at least ask the user to decide which of the three orthogonal aspects are more important for the pool they're trying to create.

I think the wizard does that, but I haven't verified the results.

 

[jgreco]

I *know* the wizard does that, but I'll agree that it isn't sufficiently intuitive to make it clear what it is doing. Sigh.