PCI Express Storage Solutions in the Data Center
Faster and less-expensive solid state drives stand to change the mechanical storage expectations of the modern data center. Current connection standards are creating a performance bottleneck that is unable to keep pace with SSD speed gains. To combat this problem, storage device manufacturers are looking at new ways of connecting storage devices to computer systems.
Limits of SAS and SATA
Peripheral connections are often the main data bottleneck point in computers. In the case of data storage, high-performance SSDs will eventually surpass the available data transfer bandwidth found in the currently used SATA and SAS connection standards. Third-generation 6.0Gbps SATA devices can transfer data up to around 515MBps in real-world use, which is enough to handle current, single SSD speeds. The third-generation SAS connection standard offers a theoretical 12Gbps bandwidth, or twice the transfer speed of SATA. However, servers need to combine multiple SSD and hard disk drive devices to max out the available bandwidth, making that level of performance an expensive investment.
Performance Potential from PCIe Storage
A storage device that’s connected to a PCIe 3.0 x4 connection can take advantage of a blazing data transfer rate of up to 3.94GBps, which is about eight times as fast as SATA. While the ports are commonly used for GPU devices, a PCIe 3.0 x16 slot offers an incredible 15.76GBps of bandwidth. This means the PCIe 3.0 standard has the potential to offer faster data transfer rates from a singular device than 30 high-end SSDs sequenced in a RAID 0 array. PC World found that combining multiple SSDs into a RAID 0 delivers up to an 88% performance boost than what a single device can offer; however, this method requires an unreasonable amount of devices to achieve similar performance from PCIe. A server would need to use eight RAID 0 SSDs to match the performance potential from a single PCIe 3.0 x4 connection.
The HDD Cap
Data centers that are using HDD technology to store data don’t have anything to gain from PCIe speeds. In real world use, a second-generation 3Gbps SATA connection will cap out at 225MBps when accounting for things like encoding. This means that 3Gbps SATA is sufficient to handle even the fastest HDDs, which peak at around 180MBps. Current 6.0Gbps SATA technology nearly three times more bandwidth than the fastest HDDs can utilize.
Looking Ahead to DIMM
The faster data access journey doesn’t end at PCIe. Modern computers rely on mass storage devices (like HDDs and SSDs), RAM, and CPU cache to handle memory functions. Intel’s in-development “Optane” technology aims to change this model by providing a mass storage solution that has data-access speeds as fast as system RAM. While this new storage platform will initially use PCIe slots for lightning-fast access, Intel plans to eventually connect Optane through RAM DIMM slots, effectively merging RAM and SSD functionality into a single component.
Instead of having dozens of SATA ports or SAS device connections, future server motherboards could be manufactured very differently than they are today. Instead the motherboards could end up sporting a dozen PCIe slots or only feature DIMM slots to handle data demands.
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