Eric Sloof just published a very interesting article about PowerPath/VE. Following up with one of my previous post about the same subject, I would like to add some info and summarize what does PowerPath/VE compared to ESX’s native multipathing.
First we must understand 2 definitions:
-Multipathing: maintains more than one physical path between the host and the storage device. If any element in the SAN fails, or at the host, such HBA, cable, switch, the host can switch to another physical path that DOES NOT use the failed component. This process is called path failover.
-Load balancing: is the process of distributing loads across multiple physical paths.
ESX4 natively supports multipathing (NMP) only, no load balancing functions here. Actually ESX4 and former versions, see the storage device in an Active/Passive way. Only one path at a time is used to send data from the host to a storage device, so basically only one path out of your 2, 4 or more paths is used. Failover is triggered by one of the 3 available policies; fixed, most recently used path and round robin. N.B. round robin is meant for production in vSphere only (ESX4).
To add load balancing support, you must install a Multpath Plug-In (MPP) that uses the vStorage APIs for Multipathing (only available in vSphere). EMC PowerPath/VE is the first to offer that plug-in.
PowerPath/VE works with VMware ESX as a Multipath Plug-In (MPP) that provides path management to ESX hosts. It is installed as a kernel module in the vSphere host (ESX host). It will plug in to the vSphere I/O stack framework to bring the advanced multipathing capabilities of PP/VE including dynamic load balancing and automatic failover to the vSphere hosts.
In few words, it enhances default ESX’s multipathing function and add dynamic load balancing to vSphere.
Now the cherry at the top of the cake, you can trade in your physical PowerPath licenses for PowerPath/VE licenses in most cases, so it can be very low cost (in some cases free).