I had an email from Bart Van Der Beek earlier this week questioning an aspect of my kit list for a Hyper-V cluster that is using a SOFS with Storage Spaces for the shared cluster storage. I had added RAM to the SOFS nodes to use for CSV Cache. Bart had talked to some MSFT people who told him that CSV Cache would not be used with tiered storage spaces. He asked if I knew about this. I did not.
So I had the chance to ask Elden Christensen (Failover Clustering PM, TechEd speaker, and author of many of the clustering blog posts, and all around clustering guru) about it tonight. Elden explained that:
- No, CSV cache is not used with tiered storage spaces where the heapmap is used. This is when the usage of 1 MB blocks is tracked and those blocks are automatically promoted to the hot tier, demoted to the cold tier, or left where they are on a scheduled basis.
- CSV Cache is used when the heapmap is not used and you manually pin entire files to a tier. This would normally only be used in VDI. However, enabling dedupe on that volume will offer better performance than CSV Cache.
So, if you are creating tiered storage spaces in your SOFS, there is no benefit in adding lots of RAM to the SOFS nodes.
Thanks for the heads up, Bart.