Generally, the market believes there are four tier 1 storage array suppliers (Wikibon Tier-1 definition) – EMC, Hitachi, HP (OEM from Hitachi, SAS-only), and IBM. Three of them (IBM, Hitachi, and HP) have announced tier 1 storage arrays with 2.5 inch SAS drives, which provide both performance and environmental benefits for performance configurations. Wikibon analyzed the space, power and cooling requirement of the arrays deploying 2.5 inch SAS drives and compared those to arrays using 3.5 inch FC drives, both for performance and capacity configurations. The configurations were defined as:

• Performance Configuration – a tier 1 configuration with 2,000 600GB drives using 2.5 inch SAS drives, where available, or 3.5 inch FC drives (a total of 1.2 Petabytes).
• Capacity Configuration – a tier 1 configuration using the densest drives available to provide the equivalent of 2,000 2 terabyte capacity drives (a total of 4 Petabytes).

These configurations were chosen to "envelope" the space, and are the maximum configurations possible. This makes comparisons between vendors easier, but they do not represent the average size of array deployed in a data center.

The methodology and assumptions used were as follows:

• The space and power requirements were derived from vendor specification sheets.
• The maximum configuration was used for each frame. The maximum power was reduced by 10% for all vendors to calculate a more accurate estimate of the actual power consumed.
• A reduction of 4.2kW was made when 2,000 SATA drives were used in capacity configurations for all vendors that used SATA disks - because SATA drives use less power.
• The PUE (Power Usage Effectiveness) of the machine room is assumed to be 2.0.
• The cost of power is assumed to be $0.12/kWhr.
• The cost of machine room space is assumed to $150/sq.ft./year.
• The ratio between the total space required (equipment space and service space) and the equipment space is assumed to be three (3) for all vendors.
• The drive capacity for SAS and FC drives is assumed to be 600GB.
• The drive capacity for SATA drives is assumed to be 2,000GB.

Performance Configuration

Figure 1 shows the results for the tier 1 performance configurations.

Figure 1 – Comparison of Tier 1 Power & Space Costs over 3 years for a Performance Configuration (600GB drives, 2.5" SAS where available otherwise 3.5" FC drives)
Source Wikibon 2010 ²

The chart clearly shows the environmental advantages that 2.5 inch SAS drives offer over 3.5 inch FC drives. The IBM 8800 and the Hitachi VSP/HP P9000 use 2.5 inch SAS drives and provide the lowest 3-year costs. The Hitachi VSP and HP P9000 2.5 inch SAS configurations are best-of-breed with a three-year cost of $180,000, less than half the cost of 3.5 inch FC configurations.

Capacity Configuration

Figure 2 shows the results for the Tier-1 capacity configurations with 3.5 inch 2TB SATA drives, or in the case of the IBM 8800 and the HP P9000, 600GB 2.5" SAS drives.

Figure 2 – Comparison of Tier 1 Power & Space Costs over 3 years for a Capacity Configuration (2TB 3.5" SATA drives or 600GB 2.5" SAS drives)
Source Wikibon 2010 ²

The IBM 8800 is the only 2.5 inch SAS-only tier 1 array, and it required seven arrays to achieve the same capacity that the EMC VMAX can achieve in one array. The IBM configuration has additional performance to spare with seven array controllers and SAS disks, but pays a huge environmental price of more than $1 million over three years. This clearly shows that for pure capacity, 2.5" SAS drives have not yet matured.

The Hitachi VSP can be configured with 3.5 inch or 2.5 inch drives. When configured with 3.5 inch SATA drives, it needs two arrays to reach 2,000 drives. However, it is still $100,000 lower in environmental cost than its nearest competitor, the EMC VMAX.

Action Item: The 2.5 inch SAS disks are clearly environmentally more cost-effective than 3.5 inch FC disks for tier 1 performance environments. For tier 1 capacity environments, 3.5 inch SATA disks are clearly environmentally more cost effective than SAS. As volumes of 2.5 inch SAS drives increase, the days of high-performance 3.5 inch FC disks are numbered. For mixed environments, the ability to intermix SAS and SATA drives offers the most flexibility.¹

From an environmental perspective, the Hitachi VSP, which allows the intermixing of SAS and SATA drives and has the lowest environmental costs for both performance and capacity configurations, is currently the "green" best of breed tier 1 storage array.

Footnotes:
¹ The comparison of FC and SAS above is for the back-end connection of disk drives in an array. For Tier 1 arrays, FC will continue to be the front-end connection to the storage network infrastructure and servers.

² The charts were updated 3/17/2011 to correct some minor errors and reflect the latest data. The HP P9000 was also included in both charts. There is no change to the relative "green" ranking of Tier 1 arrays.