How data is read\written and MPIO questions

[Sbrown]

So basically ESXi is severely handicapped when using more than 2 nodes (3 with NR5) since it would have to guess which nodes to write/read to ?

Is there any way to maintain cluster-wide cache coherency ?

[oikjn]

I don't know if I would go so far to say severely, but yes, the HP DSM is more efficient.  

Likewise there is little/no advantage to cache coherency since the read hit rate is likely very low on large datasets.

Avoid NR5 for anything but static archive data.

[HPSupportHelp]

Late reply, been away for a bit.

Excellent description.

WRT the gateway,  HP DSM makes it a moot point.

So when I look in the CMC at the sessions tab of the cluster,  what exactly is this gateway connection column telling me?  Is this the management connection?

[oikjn]

that is telling you what node that specific iSCSI connection is connected to.  When you have the HP DSM setup correctly you will see a connection from each server NIC to one node IP (thats the initial iSCSI connection and only used to initially establish the other DSM connections) and then you will see a bunch of connections saying something like "VSA_NAME (X.X.X.X),DSM".  The number of those connections would be the number of server NICs you setup with MPIO connections times the number of Nodes in the SAN Cluster, so if you have two server NICs and three nodes, you will have 6 DSM connections and two connections that don't show as "DSM"

[HPSupportHelp]

So does this connection come after a host has made the initial connection do the storage node acting as the VIP?

[oikjn]

if you are actively watching the iSCSI connection tab when you setup a new target, you will see the initial iscsi connection that doesn't show a label "DSM" and then in a couple seconds you will see additional iscsi connections generated marked as DSM.  This assumes you use the HP DSM and its setup as the guide says and you change the MPIO setting to round robin (from Vendor Specific).

[HPSupportHelp]

Thanks to oikjn and a_o for your help in answering my queries.  Very helpful indeed.

Thanks