The Oracle white paper "Exadata Smart Flash Cache and the Sun Oracle Database Machine claims that the Sun Oracle Database machine, comprising Oracle Exadata Storage Server Software and the Exadata Smart Flash Cache, is capable of meeting the extreme demands for performance and scalability required for in Online Transaction Processing (OLTP), Data Warehousing (DW) and consolidated, mixed database workloads.
While not specifically a disk replacement solution, the intelligent Oracle Exadata Storage Server Software, determines both how and when to use Flash storage and deliver the benefits of flash performance straight to the application.
The paper notes that traditional storage arrays have many internal and network bottlenecks that prevent realizing the benefits of flash. Although flash can be added to storage arrays, they still cannot deliver much of the potential performance to applications.
Which is where the Sun Oracle Database Machine demonstrates is unsurpassed utility. The solution delivers 50 GB/sec of bandwidth from flash in Exadata V2, a rate drastically higher than other solutions, and one that is on uncompressed data. Combine this bandwidth with Exadata and Oracle Database compression and offload processing, the paper continues, and an effective bandwidth is delivered that is much higher.
Oracle's use of flash PCle cards in Exadata v2 overcomes the acute bottleneck situations that result in the combination of flash disks and storage arrays, thus overcoming the limitations imposed by a slow disk controller. Exadata storage, the paper contends, can deliver close to 1GB/sec of throughput from each flash card, scaling that performance linearly across the 4 cards in every Exadata Storage Server.
The paper explains that by implementing a smart flash cache directly in the Sun Oracle Exadata Storage Server the Exadata Smart Flash Cache can allow frequently accessed data to be kept in very fast flash storage while keeping most of the data in very cost effective disk storage. This data allocation happens automatically without the user having to take any action, resulting in what the paper labels the ultimate Information Lifecycle Management (ILM) solution.
A further benefit of this solution is that Oracle allows the user to provide directives at the database table, index and segment level to ensure that specific application data is kept in flash. Tables can be moved in and out of flash with a simple command, according to the white paper, without the need to move the table to different tablespaces, files or LUNs as users must with traditional storage using flash disks.
The paper illustrates the performance delivered by the Sun Flash Accelerator F20 PCIe Card in a table that shows results ranging from a machine full rack, a half rack, a quarter rack and a basic system. The range extends from 5.3 TB down through 384 GB, with similarly dramatic capacities in the areas of uncompressed and compressed bandwidth rates and in both SATA disk IOPS and Flash IOPS.
According to the paper, "With 5.3 TB of flash storage in a Full Rack configuration, the Oracle Database can perform up to 1 million IOPS (of 8K database blocks). In many cases the entire database will reside in the cache providing performance without the mechanical limits of standard disk technology. When multiple Full Racks are joined, via the provided InfiniBand fabric, hundreds of terabytes to petabytes of data can be stored in a single Database Machine. For each Full Rack added to the configuration 5.3 TB of flash storage is included scaling capacity and performance in lock step."
The paper also discusses the two methods available for manually using and managing the cache: pinning objects in the Flash cache; and creating logical disks out of the flash for the permanent placement of objects on flash disks.
The solution also features safeguards against hardware failure in a two-fold manner. Spreading the flash cache across 4 PCIe cards mitigates some of this risk, the paper explains, adding that, if one of the flash cards should fail, the Exadata Storage Server Software automatically detects the loss of the card and takes the failed portion of the flash cache offline, all the while continuing to operate and serve data from the remaining cache. Thus, all the data is persistently stored and protected on the regular disks in the system, resulting in no data loss.
Not only can the Exadata Smart Flash Cache more than double the scan rate for data in warehouse or reporting applications, the paper concludes, it can also, by knowing what data to cache and how to automatically manage the cache, entitle the Oracle Database with its Exadata Smart Flash Cache to be labeled "the first and only flash-enabled database."
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