Question about I/O and network traffic

[ES_mycro]

Hello,

we have a 4-node P4000 multisite (Network raid 1+0, 2 sites, 2 node per site, FOM) with a vmware esxi 5.0 cluster (2 nodes, one for each site) and I have two easy questions for you which I can't find answer anywhere.

When I create a volume on a site, is this volume "possibly" (not always) spanned over the 2 Lefthand nodes (which are in a raid0 if i'm not so wrong and therefore seen as a single entity) of the site which manages it i.e. for improving I/O, or it is all created in a single node of the couple?

The network question depends by the above answer: if the volume is spanned over the pair of nodes who manage it, is the iSCSI network traffic regarding this volume done by a single node or both?

Thank you for your help.

E.

[Bart_Heungens · Accepted solution]

Hi,

The storage nodes are in the 2 sites configured, but are also the ESX hosts in the sites defined? Because this is not mandatory and will have an impact on the trafic...

First: with network RAID 10 all data blocks are written twice, so on 2 storage nodes... First block on node 1 and 2, second block on node 2 and 3, third block on node 3 and 4, fourth block on node 4 and 1, and so on...

Now if you have 2 sites, those blocks will be automatically written across the 2 sites for redundancy... What happens in the background is actually that nodes 1 and 3 are in 1 site and nodes 2 and 4 in the other site... Draw the picture with the blocks and you will see the theory behind... It is also well explained in the Lefthand training material...

Second: Windows servers have the advantage by using the DSM that that Windows server will open iSCSI connections to all nodes...

For VMware there is no DSM available at this moment. This means that your VMware host will open up 1 iSCSI connection for a iSCSI volume on 1 specific node and will keep it as long as that node will stay active...

So for VMware it is hosted by a single node... Be aware that this can be in the other site and so your ISL link between the 2 sites can be (heavily) used...

Kr,

Bart

[ES_mycro]

Bart,

yes the two Esx hosts are also defined in the Lefthand sites.

Whats the difference between having those in the site or not?

Thank you!

[Bart_Heungens]

Hi,

When the servers are also site aware they will do I/O preferencing based on the site they are located in... So they will less use the ISL between the sites...

If the servers are not site aware they will try to use any storage node...

Kr,

Bart

[CRiiser]

And for now - if you have good bandwith between sites and low latency. consider not having the esx servers assigned to an site.

Kind regards,

Christian