The IBM XIV consists of standard volume components - no hardware has been specifically designed to support storage arrays. The disk drives are standard one terabyte SATA devices. The processors and cache are standard Intel architecture. The Ethernet cards, FC and iSCSI ports are industry standard. There are three UPS’s designed to preserve cache integrity.
Lack of custom hardware in the XIV is mirrored by the lack of custom configurations. It is the model-T of storage arrays; it comes with 180 drives; if you want fewer, you still get 180 drives. You just get less space on all the 180 drives, and have to promise to buy the additional space soon. The only optional feature seems to be the power cord.
The use of purpose designed components is widespread in arrays. For example, DataDirect use special FRUs to allow a deep pipeline of data being read or written, and allow errors in that data to be corrected in flight without having to reread the data. The benefit is blistering sustained 6GB/sec read and write speeds, which is important to certain high-performance applications such as feeding supercomputers and movie making. The disadvantage is the development and maintenance cost of specialized hardware and the drag in the speed of adoption of new technology. Most other vendors use a similar custom approach to speeding up the hardware of storage arrays.
IBM is betting that that in the long run using standard components and putting development resources into software will allow the fastest evolution, fastest time to market and the overall most cost-effective solutions. The one great advantage of this approach (also taken by HP’s StorageWorks 9100 Extreme and EMC with Hulk) is a lower cost of storage. Early reports suggest that IBM is coming in at about $3-4 per gigabyte for block storage on the XIV, which is very competitive with modular storage for the functionality delivered.
However, there are a number of important consequences of this approach:
- Using standard components requires additional hardware with higher power requirements than custom hardware
- Standard components will not produce the highest performance in any category
- To reach the highest levels of performance with standard components mandates a clustered controller approach, with additional overhead and complexity
These negative consequences are illustrated by the higher environmental costs as shown in Figure 1. This is a comparison of like configurations of 180 1TB disks with 120GB of cache; the assumption is that two centralized custom controllers with 120GB of centralized cache will perform about the same as the distributed commodity controllers and 120GB of distributed cache. In a RAID 1 environment, the space costs of the alternative arrays evaluated from 3PAR, EMC & Hitachi were higher because they took two frames (except for 3PAR). However, the cost of power and cooling is higher on the IBM XIV, and overall the four-year environmental cost is $18,500 higher over four years. The main reasons for this higher energy costs are commodity components requiring higher number of controllers, and three high-function UPS modules.
In a RAID 5 configuration, all the arrays required only one frame. Because fewer drives were required for RAID 5, all the alternative configurations had lower environmental costs, an average of $31,000 over four years. RAID 5 is not available on the IBM XIV, so RAID 1 was used in the comparison.
The arrays from 3PAR & Hitachi have similar functionality that would impact storage utilization (full virtualization, thin provisioning and virtual copies). The EMC arrays have thin provisioning functionality and more limited virtualization. The established arrays have richer functionality overall, especially in remote recovery.
Action Item: The key benefits of the IBM XIV are cost, simplicity and ease of use. The performance will usually be “good enough”. The environmental costs will be little higher than custom hardware. IT executives should include all these factors when evaluating the IBM XIV and other full virtualization systems. Wikibon believes that there will be many workloads were the additional environmental costs will be significantly outweighed by lower storage administration costs and faster time to implement change.
Footnotes: This evaluation was made using generic power specifications and are not directly indicative of the power consumption of the IBM XIV product. The analysis assumes like-to-like cache and SATA disk configurations and does not account for the potentially higher capacity utilization of XIV and possible higher performance using SATA-only configurations.