Hi,
I have been looking at ways to optimise our use of storage on our VSAN cluster, as the amount of data being stored seems disproportionately high (we have about 30TB of storage and our "VM overreserved" is running around 3.6TB). On checking it appears that since we are using the default RAID1 config (FTT=1), with the default settings we are holding 2x copies of the swap files for each VM, which is running to quite an amount of disk space as some VMs have > 32GB of RAM.
As such I'm considering enabling sparse swap, but I'm not 100% clear on the implications of this, other than the obvious benefits of lower storage use.
Specifically, I am interested to know:
- With only a single copy of swap - what happens if the storage in that host dies and that object is inaccessible? Presumably the VM must crash as it can't access the pages of RAM that have been swapped out?
- We don't over-commit RAM, so presumably regardless of the above, this is a fairly low-risk change for us
- When disabling this cluster-wide, presumably it will result in a large amount of data being removed from VSAN, which will necessitate a disk rebalance. Are there any other considerations?
Thanks very much in advance for any insight into this setting.
George