Architecting a vSphere Compute Platform : Planning Host Deployment : 6.2 Boot from Local Disk
   
6.2 Boot from Local Disk
Booting from local server disks is the most traditional mechanism for the ESXi system image. However, with more and more enterprise-level servers, such as the HP ProLiant BL490c (Intel) or BL495c (AMD), geared towards virtualization and so having to maximize physical memory space, they do not come with space for internal disks. For these server hardware types (typically blades), the hypervisor can either be booted from SAN, from a USB memory stick, or from an SD memory card.
Table 9. Advantages and Drawbacks of Boot from Local Disk
Advantages
Drawbacks
Simplicity – A known entity for data centers to adopt, with both HDD and SSD supported.
VM Swapping – You can configure an ESXi host to use local storage for virtual machine swap files. This reduces load on the SAN and can improve performance under some workloads. Because these swap files are small in size, and temporary in nature, you can use small (70 GB to 150 GB) 15k RPM SAS drives to get good performance for a low price.
Flash Cache – New in ESXi 5.5 was VMware vSphere Flash Read Cache™, which allows you to use SSDs local to the ESXi host to intelligently cache VM data. This reduces load on the SAN and improves performance for VMs. This is not cheap, but it can speed up some workloads significantly. While the same disks cannot be used for flash cache and as a boot device, investment in one could lead to investment in the other.
Higher cost compute nodes – Due to the need for locally installed disks.
Higher power consumption per compute
node – Due to increased power requirement for local disks.
More heat generated by server – As a result of heat generated by spinning disks and additional power consumption.
Additional disk types to manage – Additional standby hardware to be kept in stock.
Moving parts on compute nodes – The meantime to failure of spinning disks is relatively low compared to other hardware types. Replacing disks might increase operational costs (HDD spindles only).