Understanding the Boot process in PVS:
When a target device starts it needs to somehow be able to find and contact a provisioning server to eventually stream down the appropriate vDisk.This information is stored in a so-called Bootstrap file named ARDBP32.BIN. It contains everything that the target devcie needs to contact a pVS server so that streaming process can be initialized.
The boot strap file be delivered through a TFTP server, this also partly applies to the alternative BDM(Boot Device Manager)approach. There are some distinct differences between TFTP and BDM
When using TFTP , target device needs to know how and where it can find the TFTP server to download the bootstrap file before connecting PVS server. TFTP can be configure in HA through Netscaler to avoid single point of failure. Provisoning services has its own built-in TFTP server. However, we are free to use whatever you prefer.
One of the most popular approach in delivering TFTP server address to your target devices is through DHCP, but there are other option as well..
BDM(Boot Device Manager)
There are actually two different methods to make use of the Boot Device Manager.
Let start with PVS, PVS offers a quick wizard which will generate a relatively small .ISO(around 300KB). Next , you configure your Target devices to boot from this .ISO file, using their CDROM/DVD players. This method uses a two-stage process where the PVS server location will be hardcoded into the bootstrap generated by BDM. The rest of the information like the (PVS device drivers) is downloaded from the PVS server using a TFTP protocol (UDP port 6969), here TFTP will still be used.
As of XenDesktop version 7.x, when using XenDesktop setup wizard we can create and assign a small BDM hard disk partition, which will be attached to the virtual machine as a separate virtual disk. Using this method the above mentioned two-stage approach is no longer needed because partition already contains all the PVS drivers. This way all the information needed will be directly available without the need of PXE,TFTP & DHCP.
As and added advantage using the BDM method will also decrease the boot time by around 5 to 10 sec since we don’t have to wait for PXE and TFTP