NX/XD & LAHF/SAHF

NX/XD 

The AMD No eXecute (NX) and the Intel eXecute Disable (XD)

                 NX/XD is enabled or disabled in the server BIOS and is typically found under Processor options and labeled as something like “Execute Disable Bit”, “NX Technology” or “XD Support”.

               A vital aspect of virtualization is isolation -- preventing application code in one VM from accessing the memory space used by other VMs. The idea is that when a memory area is marked as non-executable, the processor will refuse to run any code in those protected areas. This prevents one VM from affecting another VM.

LAHF/SAHF

              LAHF stands for Load AH from Flags and SAHF stands for Store AH into Flags.

              LAHF & SAHF are used to load and store instructions for certain status flags. similar to NX/XD which can be enabled or disabled in the server BIOS, support for LAHF/SAHF is typically tied into the Virtualization Technology (VT) option in a server BIOS which is often referred to Intel VT or AMD-V which is their respective support for virtualization CPU technology.

VMware Fault Tolerance

How Does VMware Fault Tolerance Work?

                  Using vLockstep Technology, VMware FT maintains a mirrored secondary VM on a separated physical Host that is kept in the Lockstep with the primary VM.If the physical host on which the primary VM fails, the secondary VM can immediately step in and take over without any loss of connectivity. VMware FT can work in conjunction with VMotion, but it cannot work with DRS

                  The primary and secondary virtual machines appear as a single entity  and access a common disk, both  running with the single IP address, Mac address but writes are only performed by the primary virtual machine.

Version recap :

FT Technology :

Record/Replay 

           Record/Replay works by recording the computer execution on a VM and saving it as a log file. It can then take that recorded information and replay it on another VM .

Fast Checkpointing 

           It copies active memory contents from Primary to Secondary via FT logging network on a continuous basis and hence a 10G network is recommended.

What is FT Logging Traffic?

             FT logging is the one of option in VMkernel port setting which is similar to enable vmotion option in the vmkernel port. when FT is enabled for the virtual machine, all the inputs (disk read.. wirte,etc..) of the primary virtual machine are recorded and sent to the secondary VM over via FT logging enabled VMkernel port.

 

What happens when you enabled Fault Tolerance for your virtual machine?
                         When you enable Fault Tolerance for the virtual machine, a secondary virtual machine (live shadow image of the primary) will be created to work with the primary virtual machine in which you have enabled FT.  The primary and secondary virtual machine resides on a different ESX hosts in the cluster.