In recent years, storage area networks (SANs) and network-attached storage (NAS) have become increasingly popular due to their scalability, utilisation and data management capabilities. But there are many instances where using a SAN or NAS to deliver high performance can prove too expensive, and direct-attached storage (DAS) can prevail as the more cost-effective solution.
Despite the popularity of SAN and NAS, DAS technology has not stood still, but has continued to evolve. Database administrators (DBAs) can now create very large DAS configurations with hundreds of drives through the addition of serial-attached SCSI (SAS) expanders and switches. At the same time, the addition of management tools using graphical user and command line interfaces has made DAS administration much easier.
It's true that DAS suffers compared to networked storage in terms of how it uses resources, and can result in unused spindles. However, it can deliver significant performance benefits for applications running software with expensive per server licences. In addition, DBAs can deploy spare spindles to isolate database objects for better performance and allocate them over more spindles to reduce latency and increase I/O operations per second.
There's also a benefit in terms of operational expenditure. With SAN or NAS, the requirement for a storage administrator role can inflate OpEx to the point where it dwarfs the CapEx. By using Oracle's automatic storage management (ASM) system with DAS, ongoing OpEx costs can be diminished. On the CapEx side, DAS has no need for the HBAs, switches and other infrastructure attached to SAN/NAS environments.
The resurgence in DAS interest from small, medium and large businesses alike is prompting many manufacturers to introduce DAS solutions or add DAS support to existing products. One approach is to combine DAS with solid state storage, RAID data protection and intelligent caching technology to accelerate performance by continuously placing 'hot data' (the information being accessed most frequently) in the onboard flash cache.
There are a number of reasons for this DAS revival. Top of the list is performance. With significantly lower latency, DAS can outperform many forms of networked storage. It helps that it is often far easier to implement and manage compared to SAN and NAS. And by minimising the requirement for SAN or NAS storage systems (and their associated host bus adapters), organisations can achieve significant cost savings.
Viewed in this light, it's no surprise DAS is becoming the preferred option for Oracle databases. In addition to getting the most from software licences by delivering superior performance in database servers, it is simpler to administer, especially using Oracle's ASM system. Some solutions also enable DAS to be shared by multiple servers.
DAS is becoming attractive at a time when Oracle DBAs are being confronted with significant changes in responsibilities. For example, trying to improve performance by minimising I/O waits in a typical database using hard disk drives (HDDs) requires a number of actions, such as shifting hot data files to cold disks or moving hot data to a higher performance storage tier, such as HDDs with faster spindles or solid state drives (SSDs).
To achieve this, the DBA needs to engage in constant, labour-intensive fine-tuning to determine what constitutes hot data, through consistent evaluation of the database and adjustments to optimise performance. One way around this is to use server-side flash storage solutions that plug directly into the PCIe bus and integrate intelligent caching with support for DAS in RAID configurations. This allows intelligent caching software to automatically and transparently move hot data from DAS HDDs to fast, on-board NAND flash memory, while retaining less frequently accessed data on HDDs.
Complementing DAS with intelligent server-side flash cache acceleration cards helps to minimise I/O latency and maximise IOPS. It also helps organisations deploy a more cost-effective mix of high-performance flash and high-capacity HDD storage to optimise the cost per IOPS and cost per gigabyte of storage.
Even better news for many organisations is that the benefits of server-side flash caching solutions are not confined to DAS. These solutions can also improve performance in SAN environments and deliver significant reductions in response times and dramatic increases in transaction throughput. This means that no matter what storage environment organisations own, they can deploy server-side flash and intelligent caching to maximise their performance in a cost-effective manner.
Tony Afshary is the business line director for Nytro Solutions products at LSI's accelerated solutions division.
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