Do you know the advantages and disadvantages of the six different use cases for SSDs?

Marc Staimer, founder and senior analyst at Dragon Slayer Consulting, has just published an excellent primer on locating SSD storage within a server and storage network. With the advent of PCIe-based SSD storage based on NAND Flash memory, the number of alternative uses for SSDs has grown and Staimer lists six such uses, plus the pros and cons for each use.

Here’s a brief summary of Staimler’s six use cases plus the advantages and disadvantages of each (see the full 2-part article for more in-depth information, registration needed):

1. PCIe SSD as server cache or storage

Advantages:

• Low latency: no intervening adapters, transceivers, cables, switches, or controllers
• Significantly improves transaction performance

Disadvantages;

• Increases CPU utilization from 5% to 25%
• Relatively low capacity caused by physical volume limitations
• PCIe SSD cards in a server can’t be shared by multiple servers
• Can’t be used by virtual servers

2. PCIe SSD as cache in a SAN or NAS storage system

Advantages:

• Reduces latency from applications to shared storage
• Can be shared by both physical and virtual servers
• Works well with virtual servers

Disadvantages:

• Cache size limited by the number of PCIe slots in the storage system
• Caches cannot be shared across storage systems
• May bottleneck the storage system’s CPU due to utilization load for the PCIe caches

3. SSDs with HDD form factor as NAS or as cache for a storage array

Advantages:

• Reduces latency from applications to shared storage
• Can be shared by both physical and virtual servers
• Works well with virtual servers

Disadvantages:

• Capacity limited by size of SSD
• Performance limited by SSD controller
• Cannot be shared across storage systems

4. SSDs with HDD form factor as Tier 0 storage in multi-tier NAS or storage array

Advantages:

• Reduces latency from applications to shared storage
• Requires no server resources
• Can be shared by both physical and virtual servers
• Works well with virtual servers
• Can reduce the number of HDDs needed without compromising performance or capacity

Disadvantages:

• Diminished ability to meet demand load as working sets grow
• Only benefits the storage system in which it’s installed
• Auto-tiering software increases load on the controller CPU with possible performance impact

5. SSDs with HDD form factor in an all-SSD NAS or storage array

Advantages:

• Reduces latency from applications to shared storage
• Only one storage tier—no complex tiering software to deal with
• Works well with virtual servers
• Consumes no server resources
• Reduces power and cooling requirements for storage
• Cost per IOPS conspicuously better

Disadvantages:

• Limited scalability (currently 500Tbytes or less)
• Storage controller is the bottleneck
• Cost/capacity

6. SSDs with PCIe or HDD form factor as a cache appliance on the storage network

Advantages:

• Reduces latency from applications to shared storage
• Sharable among physical and virtual servers and multiple storage systems

Disadvantages:

• Scalability may be limited to 10Tbytes or less
• Extra subsystem (cache appliance) may complicate troubleshooting