Both Storage Area Networks (SANs) and Network Attached Storage (NAS) provide networked storage solutions.Answer: A NAS is a single storage device that operate on data files, while a SAN is a local network of multiple devices that operate on disk blocks. SAN vs NAS TechnologyA SAN commonly utilizes Fibre Channel interconnects. A NAS typically makes Ethernet and TCP/IP connections. SAN vs NAS Usage ModelThe administrator of a home or small business network can connect one NAS device to their LAN. The NAS maintains its own IP address comparable to computer and other TCP/IP devices. Using a software program that normally is provided together with the NAS hardware, a network administrator can set up automatic or manual backups and file copies between the NAS and all other connected devices. The NAS holds many gigabytes of data, up to a few terabytes. Administrators add more storage capacity to their network by installing additional NAS devices, although each NAS operates independently. Administrators of larger enterprise networks may require many terabytes of centralized file storage or very high-speed file transfer operations. Where installing an army of many NAS devices is not a practical option, administrators can instead install a single SAN containing a high-performance disk array to provide the needed scalability and performance. Administrators require specialized knowledge and training to configure and maintain SANs. SAN / NAS ConvergenceAs Internet technologies like TCP/IP and Ethernet have proliferated worldwide, some SAN products are making the transition from Fibre Channel to the same IP-based approach NAS uses. Also, with the rapid improvements in disk storage technology, today's NAS devices now offer capacities and performance that once were only possible with SAN. These two industry factors have led to a partial convergence of NAS and SAN approaches to network storage.

Network Attached Storage (NAS)The primary difference between NAS and SAN solutions is the type of access protocol.

Network Attached Storage (NAS)Network Attached Storage (NAS) devices are storage arrays or gateways that support file-based storage protocols such as NFS and CiFS, and are typically connected via an IP network. These file-based protocols provide clients shared access to storage resources. This centralization of shared storage resources reduces management complexity, minimizes stranded disk capacity, improves storage utilization rates and eliminates file server sprawl.NAS vs SANThe primary difference between NAS and SAN solutions is the type of access protocol. NAS protocols such as NFS and CiFS provide shared file level access to storage resources. The management of the file system resides with the NAS device. SAN protocols such as iSCSI and fibre channel provide block level access to storage resources. Block level devices are accessed by servers via the SAN, and the servers manage the file system.Despite their differences, SAN and NAS are not mutually exclusive, and may be combined in multi-protocol or unified storage arrays, offering both file-level protocols (NAS) and block-level protocols (SAN) from the same system. The best of both worlds!Benefits of NAS NAS devices typically leverage existing IP networks for connectivity, enabling companies to reduce the price of entry for access to shared storage. The RAID and clustering capabilities inherent to modern enterprise NAS devices offer greatly improved availability when compared with traditional direct attached storage. Because NAS devices control the file system, they offer increased flexibility when using advanced storage functionality such as snapshots. With 10GE connectivity, NAS devices can offer performance on par with many currently installed fibre channel SANsKey NAS UsesTraditional use cases for NAS devices include file shares, home directories and centralized logging. Recently, as the performance and availability of NAS devices has improved, many customers are expanding the use of NAS to include storage for relational databases such as Oracle and MySQL, server virtualization environments such as VMWare VSphere, and virtual desktop solutions such as VMWare VDI.Creating a Network Attached Storage SolutionNAS is a common storage infrastructure offering in data centers worldwide. Eastern Computer has assisted many of our customers in justifying, designing, and implementing enterprise NAS solutions we can do the same for you! Along the way, we'll work with you to develop a solution that meets your needs, allowing you to: Lower acquisition and management costs Meet performance and availability requirements Handle ever increasing annual storage growth with minimal, to no impact to your business Minimize, or even eliminate the impact of backup windows Deliver operational and disaster recoveryGrowing a Network Attached Storage Network If your SAN has existed for a year or more, you are more than likely struggling with the following questions: Should I have a dedicated IP network for my NAS solution? What is the best data protection solution for my NAS environment? Does it make sense to use NAS storage with VMWare or HyperV? Is my NAS environment a good candidate for de-duplication and compression of primary storage? What options are available for archiving file system data? What features are different among NAS vendors, and how will that impact me? Should some of my data be on a NAS device, or never aging iSCSI?Eastern Computer can help answer all your SAN growth questions, and deliver an architecture that meets your business needs.Customized NAS OfferingsGiven the breadth of use cases for NAS devices, Eastern Computer can customize our NAS offerings to meet your needs. Here are some of the services delivered to our customer base: Complete Storage Audit A thorough analysis of your current storage infrastructure, along with an architecture roadmap, and ROI for investing in a SAN File System Assessment -- provides vital information about server volumes and files in heterogeneous storage networks without requiring installation of server agents. Using EMC standard tools we can identify capacity utilization, file age distribution, space consumption, last access time, last modification time, duplicate file types, and perform a file type classification. Once the analysis is complete, we present you with reports, findings, and recommendations in easy to understand format.This analysis can take as little time as an hour without impact to your production environment with minimal input from your IT administrators. Benefits: Helps in determining the aging of files and how much content is not being accessed or modified. Realize how much capacity can be reclaimed if this data were to be moved to an archiving tier. Understand what type of data resides on the servers. Single assessment that tells you all you need to know about the data residing on your file servers. What is the Difference between a Storage Area Network (SAN) Network Attached Storage (NAS)Tue 02/15/11At first glance Network Attached storage, also called NAS is not much different from a Storage Area Network (SAN). They both attach to a network, they both provide storage to computers on their network. There are some major differences between the two storage roles. However, these two things are becoming more and more the same thing.Differences in AppearanceThe first thing to look at when debating if you are using a SAN or a NAS is how the operating system sees the storage. Does the operating system see the storage as being on a remote computer? Or does the operating system see the storage as being local? If the operating system and/or programs knows the storage is not local, you are probably working with a NAS.

A good example of this is with Microsoft Windows network drives. If you map a network drive in windows you get a drive letter, but windows shows this drive as a network drive. Only the one user has access to it, and windows will not let you use this drive for many functions.

If you connect to a SAN Windows cant tell the storage is actually somewhere on the network. It treats the storage as if it was connected directly to the server. It is accessible to any user logged into the system; and you can use it just like any other drive.NAS ProtocolsWhen working with a SAN vs a NAS there are different protocols involved. When you connect to a NAS you will typically be working with Network Attached File Systems (NFS) or Common Internet File Systems (CIFS). In Windows, if you map a network drive to an NFS or CIFS volume, it will be treated as I have stated above, it is usable by the one user, and you are limited in what you can do.

In Linux/Unix network drives are treated differently. When you mount an NFS or CIFS volume it is treated much like it was a local disk and is available to all users on the system unless the file system permissions do not allow it.SAN ProtocolsWhen working with a SAN the most common protocols are iSCSI and Fiber Channel. Typically when working with the iSCSI protocol you will operate over an Ethernet network, and when working with Fiber Channel you will operate over a fiber optic network. However, this is not always the case. There is another protocol called Fiber Channel over Ethernet (FCOE). And there is nothing stopping you from using iSCSI over a fiber optic network.

FCOE operates a lot like iSCSI. iSCSI is an implementation of the SCSI protocol where the SCSI operations are wrapped in a TCP Packet and sent over the network. When the storage system receives the TCP packet, it extracts the SCSI command and executes it on the local storage. It then takes the result, wraps it in another TCP packet it sends it back to the client machine. FCOE does the same thing, only it uses the Fiber Channel protocol instead of the SCSI protocol.How do they Operate?When working with NAS storage, the client machine operates at the file level. This means when you want to access mycoolpicture.jpg your computer sends a message the NAS over the network asking for mycoolpicture.jpg, then the NAS responds by sending the file. When using a SAN you are operating at the block level.

This means the client machine cant simply ask for mycoolpicture.jpg. The client machine needs to actually tell the SAN where on the volume the file is. The operating system will send a message to the SAN asking for specific blocks on the file system. For example, if the picture is stored in blocks 5555 - 5577, then the client system would ask for blocks 5555 - 5577, the SAN would read those blocks, then send them over the network. The SAN does not know what it is reading, it is simply following orders.Shared access to a SAN or a NASDue to the nature of how a NAS works, it is not a problem to connect multiple servers to the same share on your NAS. You have to be more careful when connecting the same volume on a SAN to more than one client system.

This limitation comes from the way the SAN operates. Since a NAS shares files, the NAS device can handle things such as file locks and consistency checking. A SAN operates at the block level, and just trusts the operating system to know what it is doing with the blocks. Unless your file system is setup to allow for simultaneous access from more than one device you are asking for trouble.

For example, lets assume you have a SAN with a single volume, and you connect it to two servers running Windows 2003 Standard. Both systems see the volume and try to use it. When the first server writes files to the system, everything works fine. Then the other server modifies the files in some way, perhaps it just reads the files and updates the date accessed attribute on the file. NTFS is looking at the blocks of the file system and sees changes it did not expect. NTFS at this point may think there is something wrong with that Block and take some corrective action. At the same time the other server will see something strange happening and take the same action. In the end, you have a corrupt file.

Some file systems are designed for simultaneous access to the same SAN volume, for example the VMWare File System (VMFS). In a purely windows environment you want to make sure you never connect the same SAN volume to more than one server at a time unless you are using clustering.

When using Microsoft Clustering Services (MSCS) the cluster service knows you have a volume connected to more than one server and it ensures that the volume is only mounted on a single server within the cluster at any given time; assuming it is properly configured. This does not protect you from mounting that volume on another server outside the cluster, which would be a bad idea.Cluster Aware File SystemsAs I expressed in the previous section, you have to be careful as to which file system you use when sharing storage using iSCSI or similar protocols with more than one server at a time. A cluster Aware File System allows you to connect the file system to more than one server at a time.Below is a list of a few cluster aware file systems:OCFS2 - Oracle Cluster File system (Part of Linux Kernel)VMFS - VMWare File SystemCXFS - Clustered XFSBelow is a list of File systems which I know to not be cluster aware:NTFS - NT File SystemEXT2 - LinuxEXT3 - LinuxFat 16/32 - File Allocation Table (Used in Dos and Windows)XFS - Linux

The above lists by no means cover every file system, but does give a few examples of what you may be using. In a future article I will go over some of the good and bad elements of different file systems.

Difference between VMware ESX and ESXi 21:08 Mohammed Raffic It's been a long debate that everyone has been asked by what is the difference between ESX and ESXi. Most of the admins would have asked this question during interviews and also asked by new learners of VMware virtualization. I decided to post on the topic to give architectural difference always as to compare the different level capabilities between ESX & ESXi. What is VMware ESX ?

ESX (Elastic Sky X) is the VMwares enterprise server virtualization platform. In ESX, VMkernel is the virtualization kernel which is managed by a console operating system which is also called as Service console. Which is linux based and its main purpose is it to provide a Management interface for the host and lot of management agents and other thrid party software agents are installed on the service console to provide the functionalists like hardware management and monitoring of ESX hypervisor. Graphic Thanks to VMware

What is VMware ESXi ?

ESXi (Elastic sky X Integrated) is also the VMwares enterprise server virtualization platform. In ESXi, Service console is removed. All the VMware related agents and third party agents such as management and monitoring agents can also run directly on the VMkernel. ESXi is ultra-thin architecture which is highly reliable and its small code-base allows it to be more secure with less codes to patch. ESXi uses Direct Console User Interface (DCUI) instead of a service console to perform management of ESXi server. ESXi installation will happen very quickly as compared to ESX installation.

Graphic Thanks to VMware

Difference between ESX and ESXiESX 4.1 is the last version availability of ESX server. After vSphere 5, only ESXi is available. This comparison based out of the VMware Article

CapabilityESX ESXi

Service ConsolePresentRemoved

Troubleshooting performed viaService Console ESXi Shell

Active Director AuthenticationEnabledEnabled

Secure Syslog Not SupportedSupported

Management NetworkService Console InterfaceVMKernel Interface

Jumbo FramesSupported Supported

Hardware Montioring3 rd Party agents installed in Service consoleVia CIM Providers

Boot from SANSupported in ESXSupported in ESXi

Software patches and updatesNeeded as smilar to linux operation systemFew pacthes because of small footprint and more secure

vSphere web AccessOnly experimentalFull managenet capability via vSPhere web client

Locked Down ModeNot presentPresent . Lockdown mode prevents remote users to login to the host

Scripted InstalltionSupportedSupported

vMA SupportYesYes

Major Administration command-line Commandesxcfg-esxcli

Rapid deployment via Auto DeployNot supportedSupported

Custom Image creationNot supportedSupported

VMkernel Network Used for vMotion,Fault Tolarance,Stoarge ConnectivityManagement Network , vMotion, Fault Tolarance, Stoarge Connectivity, ISCSI port binding

VMWare interview questions and answers - HA (High Availability) 23:03 Mohammed Raffic

What is VMware HA?

As per VMware Definition,VMware High Availability (HA) provides easy to use, cost effective high availability for applications running in virtual machines. In the event of server failure, affected virtual machines are automatically restarted on otherproduction servers with spare capacity

What is AAM in HA?

AAM is the Legato automated availability management. Prior to vSphere 4.1, VMware's HA is actually re engineered to work with VM's with the help of Legato's Automated Availability Manager (AAM) software. VMware's vCenter agent (vpxa) interfaces with the VMware HA agent which acts as an intermediary to the AAM software. From vSphere 5.0, it uses an agent called FDM (Fault Domain Manager).

What are pre-requites for HA to work?

1.Shared storage for the VMs running in HA cluster2.Essentials plus, standard, Advanced, Enterprise and Enterprise Plus Licensing3.Create VMHA enabled Cluster4.Management network redundancy to avoid frequent isolation response in case of temporary network issues (preferred not a requirement)

What is maximum number of primary HA hosts in vSphere 4.1?

Maximum number of primary HA host is 5. VMware HA cluster chooses the first 5 hosts that joins the cluster as primary nodes and all others hosts are automatically selected as secondary nodes.

How to see the list of Primary nodes in HA cluster?

View the log file named "aam_config_util_listnodes.log" under /var/log/vmware/aam using the below command

cat /var/log/vmware/aam/aam_config_util_listnodes.log

What is the command to restart /Start/Stop HA agent in the ESX host?

service vmware-aam restart

service vmware-aam stop

service vmware-aam start

Where to located HA related logs in case of troubleshooting?

/Var/log/vmware/aam

What the basic troubleshooting steps in case of HA agent install failed on hosts in HA cluster?

Below steps are are taken from my blog posts Troubleshooting HA

1. Check for some network issues

2. Check the DNS is configured properly

3. Check the vmware HA agent status in ESX host by using below commands

service vmware-aam status

4. Check the networks are properly configured and named exactly as other hosts in the cluster. otherwise, you will get the below errors while installing or reconfiguring HA agent.

5. Check HA related ports are open in firewall to allow for the communication Incoming port: TCP/UDP 8042-8045 Outgoing port: TCP/UDP 2050-2250

6. First try to restart /stop/start the vmware HA agent on the affected host using the below commands. In addition u can also try to restart vpxa and management agent in the Host.

service vmware-aam restart

service vmware-aam stop

service vmware-aam start

7. Right Click the affected host and click on "Reconfigure for VMWare HA" to re-install the HA agent that particular host.

8. Remove the affected host from the cluster. Removing ESX host from the cluster will not be allowed untill that host is put into maintenance mode.

9.Alternative solution for 3 step is, Goto cluster settings and uncheck the vmware HA in to turnoff the HA in that cluster and re-enable the vmware HA to get the agent installed.

10. For further troubleshooting , review the HA logs under /Var/log/vmware/aam directory.

What is the maximum number of hosts per HA cluster?

Maximum number of hosts in the HA cluster is 32

What is Host Isolation?

VMware HA has a mechanism to detect a host is isolated from rest of hosts in the cluster. When the ESX host loses its ability to exchange heartbeat via management network between the other hosts in the HA cluster, that ESX host will be considered as a Isolated.

How Host Isolation is detected?

In HA cluster, ESX hosts uses heartbeats to communicate among other hosts in the cluster.By default, Heartbeat will be sent every 1 second.

If a ESX host in the cluster didn't received heartbeat for for 13 seconds from any other hosts in the cluster, The host considered it as isolated and host will ping the configured isolation address(default gateway by default). If the ping fails, VMware HA will execute the Host isolation response

What are the different types isolation response available in HA?

Power off All the VMs are powered off , when the HA detects that the network isolation occurs

Shut down All VMs running on that host are shut down with the help of VMware Tools, when the HA detects that the network isolation occurs.If the shutdown via VMWare tools not happened within 5 minutes, VM's power off operation will be executed. This behavior can be changed with the help of HA advanced options. Please refer my Post on HA Advanced configuration

Leave powered on The VM's state remain powered on or remain unchanged, when the HA detects that the network isolation occurs.

How to add additional isolation address for redundancy?

By default, VMWare HA use to ping default gateway as the isolation address if it stops receiving heartbeat.We can add an additional values in case if we are using redundant service console both belongs to different subnet.Let's say we can add the default gateway of SC1 as first value and gateway of SC2 as the additional one using the below value

1. Right Click your HA cluster

2. Goto to advanced options of HA

3. Add the line "das.isolationaddress1 = 192.168.0.1"

4. Add the line "das.isolationaddress2 = 192.168.1.1" as the additional isolation address

To know more about the Advanced HA Options

What is HA Admission control?

As per "VMware Availability Guide",

VCenter Server uses admission control to ensure that sufficient resources are available in a cluster to provide failover protection and to ensure that virtual machine resource reservations are respected.

What are the 2 types of settings available for admission control?

Enable: Do not power on VMs that violate availability constraints

Disable: Power on VMs that violate availability constraints

What are the different types of Admission control policy available with VMware HA?

There are 3 different types of Admission control policy available.

Host failures cluster toleratesPercentage of cluster resources reserved as fail over spare capacitySpecify a fail over host

How the Host Failures cluster tolerates admission control policy works?

Select the maximum number of host failures that you can afford for or to guaranteefail over. Prior vSphere 4.1, Minimum is 1 and the maximum is 4.

In the Host Failures cluster tolerates admission control policy , we can define the specific number of hosts that can fail in the cluster and also it ensures that the sufficient resources remain to fail over all the virtual machines from that failed hosts to the other hosts in cluster. VMware High Availability(HA) uses a mechanism called slots to calculate both the available and required resources in the cluster for a failing over virtual machines from a failed host to other hosts in the cluster.

What is SLOT?

As per VMWare's Definition,

"A slot is a logical representation of the memory and CPU resources that satisfy the requirements for any powered-on virtual machine in the cluster."

If you have configured reservations at VM level, It influence the HA slot calculation. Highest memory reservation and highest CPU reservation of the VM in your cluster determines the slot size for the cluster.

How the HA Slots are Calculated?

I have written a post about how the HA slots are calculated.

How to Check the HA Slot information from vSphere Client?

Click on Cluster Summary Tab and Click on "Advanced Runtime Info" to see the the detailed HA slotsinformation.

What is use of Host Monitoring status in HA cluster?

Let's take an example, you are performing network maintenance activity on your switches which connects your one of th ESX host in HA cluster.

what will happen if the switch connected to the ESX host in HA cluster is down?

It will not receive heartbeat and also ping to the isolation address also failed. so, host will think itself as isolated and HA will initiate the reboot of virtual machines on the host to other hosts in the cluster. Why do you need this unwanted situation while performing scheduled maintenance window.

To avoid the above situation when performing scheduled activity which may cause ESX host to isolate, remove the check box in " Enable Host Monitoring" until you are done with the network maintenance activity.

How to Manually define the HA Slot size?

By default, HA slot size is determined by the Virtual machine Highest CPU and memory reservation. If no reservation is specified at the VM level, default slot size of 256 MHZ for CPU and 0 MB + memory overhead for RAM will be taken as slot size. We can control the HA slot size manually by using the following values.

There are 4 options we can configure at HA advanced options related to slot size

das.slotMemInMB - Maximum Bound value for HA memory slot sizedas.slotCpuInMHz - Maximum Bound value for HA CPU slot Sizedas.vmMemoryMinMB - Minimum Bound value for HA memory slot sizedas.vmCpuMinMHz - Minimum Bound value for HA CPU slot size

For More HA related Advanced options, Please refer my blog post

How the "Percentage of cluster resources reserved as failover spare capacity" admission control policy works?

In the Percentage of cluster resources reserved as failover spare capacity admission control policy, We can define the specific percentage of total cluster resources are reserved for failover.In contrast to the "Host Failures cluster tolerates admission control policy", It will not use slots. Instead This policy calculates the in the way below

1.It calculates the Total resource requirement for all Powered-on Virtual Machines in the cluster and also calculates the total resource available in host for virtual machines.2.It calculates the current CPU and Memory Failover capacity for the capacity.3.If the current CPU and Memory Failover capacity for the cluster < configured failover capacity (ex 25 %)4.Admission control will not allow to power on the virtual machine which violates the availability constraints.

How the "Specify a failover host" admission control policy works?

In the Specify a failover host" admission control policy, We can define a specific host as a dedicated failover host. When isolation response is detected, HA attempts to restart the virtual machines on the specified failover host.In this Approach, dedicated failover hist will be sitting idle without actively involving or not participating in DRS load balancing.DRS will not migrate or power on placement of virtual machines on the defined failover host.

What is VM Monitoring status?

HA will usually monitors ESX hosts and reboot the virtual machine in the failed hosts in the other host in the cluster in case of host isolation but i need the HA to monitors for Virtual machine failures also. here the feature called VM monitoring status as part of HA settings.VM monitoring restarts the virtual machine if the vmware tools heartbeat didn't received with the specified time using Monitoring sensitivity.

If you are looking for more VMware interview questions Please click Interview Questions.

Thanks For Reading!!! All the Best...Posted in: High Availability, Interview questions Email This BlogThis! Share to Twitter Share to Facebook You might also like:

What is VMware Fault Tolerance?

VMware Fault Tolerance is a component of VMware vSphere and it provides continuous availability to applications by preventing downtime and data loss of Virtual machines in the event of ESX serverfailures.

What is the name of thetechnologyused by VMware FT?

VMware FT using a technology called vLocksteptechnology

What are requirements and Limitattions for ESX hosts & infrastructure components to run FT protected virtual machines in Vsphere 4 & 4.1?

Please refer my blog post onESX Host -Infrastrcuture Requirements & Limitations for VMware Fault Toleranceto see the ESX requirements for VMware FT.

What are Requirements and Limitations for Virtual Machine to Enable FT ?

Please refer myblog postonVirtual Machine Requirements for VMware Fault Tolerance

How do i check my host for FT compatibility from vSphere client?

One way from vSphere client is to run the cluster complaince check from profile compliance tab of your cluster. The below checks as specified below will be performed as part of the compliance check.

Validate that Fault Tolerancelogging NIC speed is at least 1000 Mbps.Validate that power management is supported on the hostValidate that Fault Tolerance logging is enabled.Validate that VMotion NIC speed is at least 1000 Mbps.Validate that all the hosts in the cluster have the same build for Fault ToleranceValidate that the host hardware supports Fault Tolerance.Validate that VMotion is enabled.Validate that at least one shared datastore exists

Another way is to check the summary tab of the ESX/ESXi host, "Host Configured for FT" yes or NO.

If " Host Configured for FT" is No. It will display the items required for thatparticularESX for FT to work.

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 thesecondaryVM over via FT logging enabled VMkernel port.

How to Enable FT Logging in VMkernel Port?

GO the ESX host -> Configuration-> Networking -> Properties of Virtual switch with the VMkernel portgroup configured

Click on VMkernel Port -> click on Edit -> General tab -> select the Fault Tolerance Logging -> click on OK.

How do you configure or enable FT for the virtual machine ?

FT can be enabled only per virtual machine basis not at the cluster or ESX level.

Right-click the virtual Machine -> Fault Tolerance -> Turn on Fault Tolerance

How does the FT enabled virtual machine will be differentiated with non FT VM's in vSphere client?

FT Enabled Virtual machine will appear in Dark Blue colour as compared to non-protected virtual machines.

By default, Only Primary virtual machine will appear under the cluster and ESX host. To take a look at the secondary VM , Go to Virtual Machines tab of the Cluster or Host.

How Does VMware Fault Tolerance Work?

When you enable Fault Tolerance for the virtual machine, a secondary virtual machine 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. Whatever the events or actionsperformed by the primary VM will be transmitted via gigabitEthernetnetwork to be replayed by the secondary virtual machine using VLockstep technology. Eventhough both the primary and secondary virtual machines appear as a single entity and access acommon disk, both running with the single IP address, MAc address but writes are only performed by the primary virtual machine.The primary and secondary virtual machines sends heartbeat between eachother frequently with millisecond intervals to the check for the availability. If either of the virtual machine loses the heartbeat, other virtualmachinewill take over the primary virtual machine role immediately.

GraphicsThanks toVMware.com

What happens when you enabled Fault Tolerance for your virtual machine?

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

What will happen when the ESX host of primary VM failed?

When a failure is detected on the primary VM's ESX host, the secondary virtual machine which is running on the another ESX server in the same cluster will takes the place of the first one with theleast possible interruption of service.

If vCenter is down, will the FT work?vCenter server is only required to enable FT on the virtual machine.once it is configured, vCenter is not required to be in online for FT to work. FT failover between primary and secondary willoccure even if the vCenter is down.

How does Vmware FT differs from VMware HA?

1.VMware HA is enabled per cluster basis but FT is enabled per VM basis.

2.In caseof ESX host failure, virtual machines in the failed host are restarted and powered-on on the other active hosts in HA cluster. So the restart duration of the virtual machine is the downtimefor the virtual machine in HA cluster. But in FT enabled virtual machine, there is nodowntime. In case of host failure, secondary VM will become primary and continuing the execution from the exactpoint where the primary VM is left off or failed. It happens automatically without data loss, without downtime and with a little delay. Users will not see any interruption.

How do you see the summary status of the FT enabled virtual machines in the ESX host from vsphere client?

Click on Summary tab of the ESX host -> Fault tolerance information and VM counts will be displayed

ESX is an installed software suite managed by VirtualCenter by a standalone VirtualCenter Client via a built-in VLI or web service. ESX is licensed per seat and also has to have an agent license for connecting to the VC server.ESXi is a free product that can be installed on a server's disk or embedded by a flash device. It can be managed by a VC Client or you can connect it to a VC Server.The Major difference is that ESX has a Service Console (SC) for management. ESXi does not have a service console and is much smaller and more secure.ESXi management is GUI only where as ESX management can be GUI or CLI based.