Using the local storage

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bbeachy2001
Posts: 3
Joined: Tue May 12, 2020 1:35 am

Tue May 12, 2020 1:41 am

So I'm getting ready to set up a hyperconverged scenario with Starwinds virtual appliances on several hosts. I assume we set the iSCSI connections up in vmware to use Round Robin MPIO. But, if a VM accesses a volume that resides on the same host, what is the mechanism that causes it to only use the path to the faster storage on the local host instead of the path to the synchronized storage on the other host? And does this only help read speeds, since writes still require the second copy to be written synchronously?
yaroslav (staff)
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Posts: 2279
Joined: Mon Nov 18, 2019 11:11 am

Tue May 12, 2020 4:15 am

Starwinds virtual appliances on several hosts
How many hosts do you plan to have?
if a VM accesses a volume that resides on the same host, what is the mechanism that causes it to only use the path to the faster storage on the local host instead of the path to the synchronized storage on the other host?
That's a good question. You can use FIXED to use the specific path for I/O. You can use the local path, however, it might get overwhelmed at some point. That is why we use Round Robin in most cases. Learn more at https://pubs.vmware.com/vsphere-51/inde ... 959CC.html.
And does this only help read speeds, since writes still require the second copy to be written synchronously?
Both reads and writes are affected. Synchronization is done by means of StarWind. Provided that the separate channel is used for sync, synchronization does not interfere with disk IO. The only thing you can improve is disabling delayed acknowledge (if you have 1 GBE). Sometimes it helps.

May I learn the network bandwidth of your setup?
bbeachy2001
Posts: 3
Joined: Tue May 12, 2020 1:35 am

Thu May 14, 2020 5:13 pm

I have a total of 4 identical hosts.

I intend to use Round Robin - my question is, won't some of the traffic go out over the physical NIC's to the host where the second copy of the volume is, instead of only using the path to the internal storage? Or is that not really an issue?

I have 6 10Gb NIC's on each host. 2 for network, 2 for iSCSI, and 2 exclusively for replication. I then have a pair of 10GB links between the first two hosts at one physical location, and the second pair of hosts at the second location.

My intention is to sync all volumes on host 1 at location 1 with host 3 at location 2. All volumes on host 2 at location 1 will be synced with host 4 at location 2
yaroslav (staff)
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Posts: 2279
Joined: Mon Nov 18, 2019 11:11 am

Fri May 15, 2020 1:13 pm

won't some of the traffic go out over the physical NIC's to the host where the second copy of the volume is
Traffic will go to local storage and to partner in turns. If you have configured the rescan script, one command will go to the local storage and the other will go to the partner. If you did not configure and run the Rescan Script, path switch will be done every 1000 commands. If you want to use local storage over the partner's storage, please use Fixed multipath policy.
Or is that not really an issue?
That's not an issue at all. Round Robin helps to leverage the loads on the networking and storage in your system, so it is ok to go with Round Robin.
2 for iSCSI
Please note that StarWind does not recommend to team iSCSI and Sync links. I am saying just in case you have them teamed instead of having them configured as 2 separate links.
My intention is to sync all volumes on host 1 at location 1 with host 3 at location 2. All volumes on host 2 at location 1 will be synced with host 4 at location 2
The scenario that you have just described looks like 2 separate 2-node stretched clusters. May I ask you how many physical connections (i.e., wires) going from the switch in 1 location to the switch in the second location? There should be at least 2 connections between locations for each cluster to avoid split-brain issues.
Could you share with me the network diagram here? Just want to see how everything is connected.
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