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‪#‎VMware‬ ‪#‎ESX‬ / ‪#‎ESXi‬ - explained

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Jul 24th, 2013
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  1. ‪#‎VMware‬ ‪#‎ESX‬ / ‪#‎ESXi‬ - explained
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  4. Its mainly used in production clusters and datacenter environments for running multiple VMs in a host. Unlike VMware ‪#‎workstation‬,it is installed on a bare-metal hardware. In short ESX/ESXi by itself is a ‪#‎hypervisor‬ OS. Since it runs directory on the top of hardware,it can be considered as bare metal or type-1 hypervisor. VMware ESX is the older variant and ESXi is the newer one. This content was post on http :// www. facebook .com/geeksch00l ‪#‎UnhappyGhost‬
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  6. First of all, the architecture of ESX will be explained, followed by details like “what make ESXi different from ESX and why VMware stopped development of ESX and turned towards ESXi. ‪#‎GeekSchool‬ ‪#‎GeekSch00l‬
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  8. ESX Architecture:
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  11. ESX has some linux dependencies. The VMware FAQ states: “ESX Server also incorporates a service console based on a ‪#‎Linux‬ 2.4 ‪#‎kernel‬ that is used to boot the ESX Server virtualization layer or ‪#‎VMkernel‬” . On starting an ESX host, a Linux Kernel will be started which will load some virtualization components like VMware’s vmkernel. The VMkernal is responsible for allocating memory, scheduling CPUs and providing other hardware abstraction and operating system (OS) services. This content was post on http :// www. facebook .com/geeksch00l
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  13. ESX has a Linux kernel based service console(COS) which acts as a management interface for the host. Various VMware management agents are deployed in the Console OS, along with other infrastructure service agents (e.g. name service, time service, ‪#‎logging‬, etc). We can also deploy 3rd party tools for hardware ‪#‎monitoring‬ and system management. Admins can login for configuring and troubleshooting purpose. Last and final ESX version released was VMware ESX-5.
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  15. ESXi Architecture:
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  17. In ESXi , the Console OS has been removed and included ‪#‎POSIX‬ shell which looks and works like linux but with limited functionalities. .All VMware management agents run directly on the vmkernel. Infrastructure services are provided natively through modules included with the vmkernel. Other authorized 3rd party modules , such as hardware drivers and hardware monitoring components, can run in vmkernel as well ,if and only if the modules are digitally signed by VMware .All these features together creates a tightly locked-down architecture increases the security of the system. This content was post on http :// www. facebook .com/geeksch00l
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  19. With the removal of Service Console and Linux Kernel, the disk footprint of ESXi is very less (32 MB) which is very low when compared to that of ESX(2 GB). Since size of ESXi is small,installation and booting time decreases considerably. ESXi is being sold by hardware vendors as a built-in hypervisor. That means that, say, you buy a ‪#‎Dell‬ server, ESXi can be built inside the server (‪#‎embedded‬) on a ‪#‎flash_chip‬, on the ‪#‎motherboard‬, which reduces the need for installing it in the hard disk. This content was post on http :// www. facebook .com/geeksch00l
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  21. VMware is in a phase of removing its dependencies with other vendors . It has reduced the dependency with Linux by removing the Linux kernel based COS support in ESXi.
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  23. 1)Software based full virtualization.
  24. 2)Hardware assisted full virtualization.
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  26. 1) Software based full ‪#‎virtualization‬.
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  28. Software based full virtualization in ESX/ESXi is similar to that of VMware workstation. ESX/ESXi provides full virtualization through instruction emulation.It uses two techniques ,“trap and emulate” and “binary translation” to ensure full virtualization on X86 hosts. The Virtual Machine Manager (‪#‎VMM‬) switches between the appropriate technique dynamically based on the state of the virtual CPU. In “trap and emulate” technique, guest VMs will be made to run in less privileged rings (ring 1 or 3)and all the guest instructions will be executed directly on the host CPU except some sensitive privileged instructions. All the instructions from the guest OS will be analysed by VMM/hypervisor(ring 0) ,allowing safe instructions to run unmodified and all the sensitive instructions are trapped and emulated/replaced with a set of safe instructions before executing. But some privileged instruction from guest machines,cannot be trapped in VMM. To overcome this drawback,VMware incorporated “binary translation” technique to translate the sensitive instructions which cannot be trapped by VMM. The converted code is also cached in memory, to speed up future (sensitive) instructions coming in for execution. This content was post on http :// www. facebook .com/geeksch00l
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  30. 2) ‪#‎Hardware‬ assisted full virtualization
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  32. To implement Hardware assisted full virtualization ,host machine CPUs should have virtualization extensions (‪#‎AMD‬-V and ‪#‎Intel‬-VT). This technology employs an additional “root VMM layer” under the Ring 0 of X86 ring architecture.. Ring 0 is left available for guest operating systems . Here , host CPU itself will take care of “trap and emulation” of privileged instructions from the guest OS,there by eliminating the need for “binary translation” and VMM/hypervisor based traps. This allows for guest OSes to be virtualized without any modifications. This content was post on http :// www. facebook .com/geeksch00l
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  34. VMware started employing Hardware Assisted Full virtualization from VMware ESX 3.5 release. VMware is widely using it in latest ESXi 5.1 releases after the release of 2nd generation AMD-V processor which has the memory virtualization capability. In future , hardware assist technology will eliminate the need for software based full virtualization and ‪#‎paravirtualization‬. This content was post on http :// www. facebook .com/geeksch00l
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