Comparing Dell PowerEdge Server Boot Options

When evaluating server hardware, there are many considerations that go into an architecture decision. Along with processor and memory configurations, the medium used to install and boot an operating system (OS) or hypervisor is an important design item that can vary based on use case. This article will examine the different boot options available on Dell PowerEdge Servers and look at design considerations for each.

Operating systems and hypervisors require block storage for installation; therefore, a file share using NFS or CIFS cannot be used for this purpose. Internal disk is the traditional and most common way to boot a server. This method can be accomplished by using HDDs, SSDs or SD cards. An onboard storage controller or RAID card can add redundancy to internal disk. Dell has also created an exclusive internal disk technology called the Dell Boot Optimized Server Storage, or BOSS, that is a redundant storage device optimized for booting an OS or hypervisor. Finally, external disk is categorized as block storage presented over a storage network from a SAN using iSCSI or FIbre Channel protocols. We will examine each configuration and the advantages or disadvantages to each.

Internal disk

Using internal disk for a boot drive has been the most popular option in servers due the simplicity of using disks in a server rather than external disk from a SAN. Performance of local disk is also more predictable than disk that is shared between many servers. Rack servers tend to favor local disk options as rack servers have more room in the chassis for drive bays and IO cards than a blade server would.

A disadvantage to local disk in the past has been that drivers may be required by the OS at the beginning of the install in order to detect the drives. An example of when that may be applicable is local disk that uses a RAID controller. Dell has solved this issue using their Lifecycle Controller that is built into every PowerEdge server. So when choosing a local disk option such as the Dell BOSS or a RAID card, there will not be any issues with drivers if installing the OS using the Lifecycle Controller.

Dell Boot Optimized Server Storage (BOSS)

The Dell BOSS card is a PCIe device that uses two M.2 SSD drives in a redundant RAID 1 configuration. The reason to use the BOSS card is to free up the SAS or NVMe disk slots on the server to be used by higher demanding disk workloads such as software defined storage or database applications.

Starting with Dell 15th generation PowerEdge rack servers the M.2 disks on the BOSS card are accessible and hot swappable from the rear of the chassis without opening the case. This makes ongoing maintenance easier should M.2 disks need replaced in the BOSS.

Advantages:

• External hot swappable M.2 disks on newer rack servers.
• Designed for server operating system installation.
• Leaves onboard SAS and NVMe disks slots open for data use.
• Larger disk capacities than SD.

Disadvantages:

• No battery backup. Write through only.
• No self-encrypting drive support.

Secure digital (SD) cards

Servers have used SD cards for many generations as an option for installing an operating system. It is arguably the simplest media to set up and use for an OS. Dell uses SD card readers attached to the motherboard within servers. The card reader has a controller onboard that allows for RAID-like redundancy of two SD cards.

Advantages:

• Easy to set up and configure.

Disadvantages:

• Limited capacity.
• Slower IO than traditional disks.
• No battery backup. Write through only.
• No self-encrypting drive support.
• Not hot swappable and requires opening the chassis to access.

Local disk or SSD

The oldest method for OS volumes is local disk. Traditionally these have been spinning platter disks, but SSD has become more standard in recent years. The disks attach to either a SAS or NVMe backplane to provide fast IO. When connected to a RAID card, these disks can be configured for many different levels of RAID.

Advantages:

• Disks are hot swappable.
• Larger disk capacities than SD.
• Fast IO using SAS or NVMe.
• More RAID options than RAID 1.
• Self-encrypting drive support.

Disadvantages:

• RAID card required for redundancy.
• More expensive option for local disk OS usage.

External disk

External disk from a SAN has become a favorite for blade servers in established data centers. Often there is an existing SAN and storage switching being used for virtualization and application needs. Placing boot volumes on a SAN for use with blades is good option because the boot volume can be reassigned to other servers as needed.

Fibre channel disk

Disks presented over a fibre channel network can be used for creating a boot volume. This option requires the most hardware and configuration of any of options for OS boot volumes. In addition to a SAN, a fibre channel network is required to connect hosts to the SAN. This option usually favors larger environments where a fibre channel SAN is already being used for application data.

Advantages:

• Large volumes can be created.
• Fast and reliable fibre channel protocol.
• Boot volumes can be moved between hosts.
• Boot volumes can be backed up and replicated at block level.

Disadvantages

• Most expensive option requiring SAN and fibre channel switch infrastructure.
• More complex setup and configuration.

iSCSI disk

Like Fibre Channel, a SAN can also present disk using the Internet Small Computer Systems Interface (iSCSI) protocol. An advantage to iSCSI is that it uses traditional TCP/IP for host connectivity which makes for easier configuration by not needing a separate Fibre Channel network.

Advantages:

• Large volumes can be created.
• Uses existing Ethernet network switches and host NICs.
• Boot volumes can be moved between hosts.
• Boot volumes can be backed up and replicated at block level.

Disadvantages:

• Requires SAN and fast Ethernet switching.
• May not scale for high IO needs.

Conclusion

Internal disk remains a popular option for booting servers due to low expense and easier configuration. The Dell BOSS card is especially a great option for rack mount servers due to the hot swappable access of the M.2 cards. For larger environments that have a requirement for boot volumes to be portable between servers, external disk from a SAN is needed. The Dell MX7000 Modular Chassis is a good idea when using external disk as the MX7000 supports virtual identities for stateless computing. No matter which option you choose, it is always best to install the OS using the Dell Lifecycle Controller to streamline the drivers needed by the OS.

Contact your WWT account team to learn more about the best server configurations for your needs.