RAID rebuild

A RAID rebuild is the most stressful time period in the life of a drive. This is because the drive is busy servicing IO requests to rebuild the RAID set, while also servicing normal read/write IO requests. A drive is more likely to fail during a RAID rebuild. For this reason, it's a good idea to think about smaller RAID 5 sets, use RAID 6 or RAID-DP, or employ the use of a hot spare drive along with RAID protection.
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Virtual disk to an RDM

Convert a standard virtual disk to an RDM with the following commands:
For virtual compatibility mode: vmkfstools -I [srcfile] -d rdm: /vmfs/devices/disks/vmhbaW:X:Y:Z /vmfs/volumes/[datastore]/[vmdir]/[vmname].vmdk
For physical compatibility mode: vmkfstools -I [srcfile] -d rdmp: /vmfs/devices/disks/vmhbaW:X:Y:Z /vmfs/volumes/[datastore]/[vmdir]/[vmname].vmdk
http://kb.vmware.com/kb/3443266
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Configuration Maximums

Configuration Maximums Comparison

Virtual NICs per VM:
ESX(i) 4.1: 10 NICs
ESX(i) 4.0u1: 10 NICs
ESX(i) 3.5 Update 5: 4 NICs
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vSphere 4.1

With vSphere 4.1 being the last version with a Service Console, you will need to learn how to use vMA Appliance 4.1 efficiently. Get to know vi-fastpass & its commands which are used to bind to hosts & execute commands without having to supply a server name & credentials with each command issued. vMA 4.1 eliminates the sudo requirement:

vifp addserver host
vifp removeserver host
vifptarget -s host

http://bit.ly/dp5GTL
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VM networking issues

If you are experiencing host or VM networking issues, take a look at VMware KB article 1004109 entitled ESX Server host or virtual machines have intermittent or no network connectivity. This article contains several links to troubleshoot networking issues.

http://kb.vmware.com/kb/1004109
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Configuration Maximums Comparison

Configuration Maximums Comparison

Number of virtual machines per host:
ESX(i) 4.1: 320 VMs per host (all cluster feature restrictions lifted)
ESX(i) 4.0u1: 320 VMs per standalone host
ESX(i) 4.0u1: 256 VMs per host in a DRS cluster
ESX(i) 4.0u1: 160 VMs per host in an HA cluster of 8 or less hosts
ESX(i) 4.0u1: 40 VMs per host in an HA cluster of 9 or more hosts
ESX(i) 3.5u5: 170 VMs per host
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ESX snapshots

vSphere's vDS is comprised of two components: The Control Plane (the brain) and the Data Plane (the brawn). vDS configuration and control sits the vCenter Server. This is the Control Plane. The Data Plane performs the actual frame forwarding and resides on each ESX(i) host.

http://www.vmware.com/files/pdf/vsphere-vnetwork-deployment-wp.pdf
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