Is RAM cache the same performance as a RAM disk?

[rrbnc]

In a multi-node configuration, does read cache and write buffer operate at the same IOPS as a RAM disk? I would think that read cache would operate at the speed of RAM disk because it does not need to sync to all nodes, but write buffer would not because it has to sync over the network to all nodes. Is this correct?

If so, then the network between the nodes would be a bottleneck for performance, correct? Does that mean FC would be a better choice than 10 Gb CAT6 ethernet, because latency is lower for FC? Is there something with lower latency than ethernet and FC?

I am trying to determine how to get the most performance out of SATA+RAM w/ StarWind.

[anton (staff)]

Partially..StarWind L1 caches are also synchronized between nodes for writes (always) and for reads (if there's a space). Reason is we take extensive use in a data locality so when VM moves to a "partner" node it does not start from the "cold" state when there's no I/O cached.

Partially Indeed for writes synchronization is a limiting factor so we recommend to have as "fat" back bone as you can. however latency is not of that big issue as we sync with the comparably big blocks.

We cannot use native Fibre Channel as we use iSCSI as built-in synchronization protocol (like for example MSFT uses SMB3 with Storage Spaces Shared Nothing or Live Migration). So FC is out. IB is OK (with the decent Mellanox cards IPoIB is acceptable so we get 33-35 Gbps from a 56 Gb IB link).

You really need to wait for an upcoming In-Memory version of StarWind Virtual SAN that would do what you want. Please give us some weeks for that.

In a multi-node configuration, does read cache and write buffer operate at the same IOPS as a RAM disk? I would think that read cache would operate at the speed of RAM disk because it does not need to sync to all nodes, but write buffer would not because it has to sync over the network to all nodes. Is this correct?

If so, then the network between the nodes would be a bottleneck for performance, correct? Does that mean FC would be a better choice than 10 Gb CAT6 ethernet, because latency is lower for FC? Is there something with lower latency than ethernet and FC?

I am trying to determine how to get the most performance out of SATA+RAM w/ StarWind.