Best practice for VHS size

Question

Hi, we have a 12 node Isilon cluster with two tiers on OneFS version 8.2.2.0 providing 1.72 PiB of storage. I need some advice on setting the VHS size. At the moment it is set at 10% which means we are reserving 172TiB for rebuilds if we have a failure. Our archive tier consists of A2000 nodes with 4 x 10TB disks in each sled. The 172TiB seems to me to be way too much if I am reserving for disk failures (4 would only be 40TB and likelihood of losing more than 4 disks permanently is extremely small) or not enough if I am reserving for a node failure (which would need 200TB). What do people normally set this at? Is there any rationale for setting it as a percentage of total capacity? Ian

DELL-Josh Cr · Answer

Hi Ian, It depends on your tolerance for losing a node. If losing a node is fine then you probably can reduce the VHS to 5% or 2.5% but if it isn’t you probably should increase it to 200TB.

ianmi · Answer

Thanks Josh - I agree with your response except I can't see any reason for setting it as a percentage of total provisioned. Number of disk failures - fine. Number of node failures - fine. But why would you ever set it as a percentage?

Phil.Lam · Answer

@ianmi  I know you need 10% free to do OneFS upgrades.

Isilon

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