Notes

• If a cluster of machines have their own OS hard drives, and one cannot afford a machine going down then each of the machines would need a RAID 1 config which requires a RAID card and 2 hard drives each resulting in a considerable cost (high-cost)
• In the scenario where multiple machines boot off a partition on a SAN device, the machines do not need any harddrives. However if for any reason the connectivity to the SAN goes down or the SAN device itself crashes (rare) then all the machines in the cluster would be down (marginal redundancy concern)

Conclusion

• In the scenario where the data partition of the cluster of machines is residing on a SAN device, it makes sense to boot those machines off the SAN device too since as such the SAN going down would render the entire cluster useless, and this way one can save the cost of 2x’n’ hard drives and ‘n’ RAID cards (assuming we have ‘n’ machines in the cluster)
• In the scenario that a cluster of machines does not have any data on a SAN device, one may want to invest in hard drives for the machine itself, since a downtime of the SAN device will not render the cluster inoperational. Additionally, if the cluster consists of 10-15 machines, the cost of 2 SATA drives and 1 RAID card per machine may not be much higher than the cost of a SAN device if one needs to be exclusively setup for these machines.
• This may change however if one has spare and redundant SAN devices lying around, with spare capacity in their network
• Ideally if a cluster of machines are to PXE boot off a SAN, one should try and ensure that the boot partitions are spread across separate SAN Devices each of which are accessible through different network paths, so that the downtime of any given SAN Device does not compromise the cluster