What is the iSCSI channel between nodes for?

[mpg]

What are the iSCSI channels used for within a VSAN cluster? I understand the sync channel is used for keeping the underlying storage on each node locally in sync, but I do not yet understand what the iSCSI traffic is for. An external host can talk to the VSAN cluster as if it is an iSCSI device yes? But this is not what the channel is from what I am gathering. Are they used actively by the nodes for reading data? Like if I open a 100gb file on a node out of the HA storage, will it be loaded into memory via the iSCSI network in addition to local storage? Does this "accelerate" a read or are all read/writes done locally first, then synced via the sync channel only? If it IS reading using the other nodes via network, can this actually boost the performance to what ever the network is? For example, 10gbs network is much faster than 6gbs SATA, so if I had 2 nodes, does the VSAN get performance more like 10gbs read? or 16gbs?? Many of questions! If I missed this in the documentation online please let me know where it is so I can read it, I've been going over a lot of docs but haven't understood this aspect yet.

[VMax (staff)]

Actually, most of your guesses are correct.
iSCSI channel is used to access partner node storage by iSCSI. This gives us several benefits:
- Both nodes can access local and partner storages, and using MPIO distributes read/write operation between nodes, thus, boosting perfomance.
- If hard drives or RAID fail, node will still be able to access partner storage and function properly.
- If Sync channel fails, without ability to synchronize only one node will have active storage, but again, using iSCSI channel, both nodes will have storage present.
iSCSI channel fail also won't interrupt operations, as both nodes will be synchronized and able to access storage locally.

[mpg]

That's actually amazing. I thought I was being too hopeful in my guesses, but it's even better than I thought! Thanks for the response.

[VMax (staff)]

Thank you for kind reply.
Do not hesitate to ask if any more questions about StarWind working principles will arise.