Improve Performance and Efficiency With Hybrid and All-Flash Storage
The storage industry is seeing a transition from traditional HDD to SSD using NAND flash technology. Adoption of this technology for high-performance transactional systems has reached a tipping point. Many z/OS* clients benefit from performance and efficiency gains by implementing flash storage.
The IBM DS8000* family includes both the all-flash DS8888, and hybrid DS8884 and DS8886 systems; this article describes the options available and provides tips for effective planning and implementation. It also outlines the differences between z/OS and distributed systems, and how other IBM z Systems* technologies—such as zEnterprise* Data Compression (zEDC)—complement the use of flash storage.
Flash provides significant latency improvements compared with traditional HDDs. However, it’s still slower than dynamic random access memory, so read and write cache provide significant benefits. Write cache helps coalesce and avoid repeated writes from unnecessarily wearing out the flash media. The Intelligent Write Caching algorithms on the DS8000 storage developed by IBM Research consider both temporal and spatial locality to minimize wear on the flash.
Flash can also sustain significantly higher random I/O throughput than traditional HDDs. Flash-optimized hardware, such as the high-performance flash enclosure in the DS8000 family, is important to ensure RAID systems designed for HDD don’t become a bottleneck when using flash. However, in most cases, applications aren’t actually driving the maximum random I/O throughput in flash environments but are still significantly above what’s possible with traditional HDDs.
Equally important to z/OS environments is good sequential performance for batch workloads. Modern flash media are significantly superior to earlier generation technology in this aspect—especially for sequential writes. However, a flash-based system must handle the required sequential workload as well as random I/O.
The density of flash storage has increased over the last three years to the point where significant density savings exist when compared with high-performance enterprise drives. Depending on the cost of data center floor space and the associated power and cooling, this can have a major impact on the overall affordability of flash storage.
Response Time Shrinks
In addition to the speed of the underlying storage media, several factors affect a storage system’s host response time. With the implementation of flash storage, the media response time can become a smaller percentage of the overall response time. Minimizing the other components then becomes critical to making further reductions in response time.
Moving to faster SAN fabrics, channels and host adapters can help reduce the overall host response time. Another often overlooked factor is the contribution of the protocol and software stack on the host to the overall response time. High Performance FICON* for z Systems has provided significant improvements in this area, and the DS8880 includes other enhancements to reduce latency and improve throughput for specific workloads. These include IBM zHyperWrite* for DB2* logs, the DB2 Castout Accelerator and the List Prefetch Optimizer.
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