Caching less for better performance: balancing cache size and update cost of flash memory cache in hybrid storage systems
Caching less for better performance: balancing cache size and update cost of flash memory cache in hybrid storage systems
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发表时间：
2012-02
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通讯作者：
Y. Oh;Jongmoo Choi;Donghee Lee;S. Noh
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作者：
Y. Oh;Jongmoo Choi;Donghee Lee;S. Noh
混合存储解决方案使用基于NAND闪存的固态驱动器（SSD）作为非易失性高速缓存，使用传统硬盘驱动器（HDD）作为较低级别的存储。与典型的缓存不同，在内部，闪存缓存分为缓存空间和过度配置空间，用于垃圾收集。我们表明，适当地平衡这两个空间有助于提高混合存储系统的性能。我们表明，与预期相反，该高速缓存不需要充满数据的最充分的，但可能会更好地通过保留空间的垃圾收集。对于这种平衡行为，我们提出了一个动态的计划，进一步划分该高速缓存空间到读和写缓存和管理的三个空间根据工作负载的特点，以获得最佳性能。实验结果表明，我们的动态计划提高了性能的混合存储解决方案的离线最佳性能的固定分区方案。此外，由于我们的方案有效地利用了闪存缓存，因此减少了擦除操作的次数，从而延长了SSD的使用寿命。
Hybrid storage solutions use NAND flash memory based Solid State Drives (SSDs) as non-volatile cache and traditional Hard Disk Drives (HDDs) as lower level storage. Unlike a typical cache, internally, the flash memory cache is divided into cache space and overprovisioned space, used for garbage collection. We show that balancing the two spaces appropriately helps improve the performance of hybrid storage systems. We show that contrary to expectations, the cache need not be filled with data to the fullest, but may be better served by reserving space for garbage collection. For this balancing act, we present a dynamic scheme that further divides the cache space into read and write caches and manages the three spaces according to the workload characteristics for optimal performance. Experimental results show that our dynamic scheme improves performance of hybrid storage solutions up to the off-line optimal performance of a fixed partitioning scheme. Furthermore, as our scheme makes efficient use of the flash memory cache, it reduces the number of erase operations thereby extending the lifetime of SSDs.