Freezing Frozen Pages with Multi-Stream SSDs

Abstract

Flash memory SSDs have been replacing hard disks as the main storage thanks to their high IOPS/$ and energy e ciency [6]. Internally within SSD, Flash Translation Layer (FTL) has control over data mapping and garbage collection (GC). Because of its architectural feature, log-structured approach, the costly GC operation is unavoidable to secure new blocks for newly written pages. During every GC, valid pages from the victim block have to be relocated causing additional writes. It is well known that these additional writes (i.e., write ampli cation) negatively a ect the performance and lifespan of the ash memory SSDs. Hence, it is imperative to reduce write ampli cation factor (WAF) in modern ash memory SSDs. Though numerous FTLs have been proposed with this goal in mind, the most commercial ash storage device is known to take the page-mapping FTL approach [7]. Unfortunately, it is well known that page-mapping FTL results in highWAF (e.g., 5), particularly against random write patterns which are common in OLTP workloads. Recently, one interesting interface for ash memory SSDs, called Multi-Streamed SSD (MS-SSD in short), has been proposed and standardized to lower the GC overhead with the help of explicit hint on data lifetime from applications [4, 8]. The main purpose of MS-SSD is to allow to place data pages with di erent lifetime into di erent ash regions so as to reduce the SSD-internal WAF from GC. Meanwhile, the e ectiveness of MS-SSD is highly dependent on the accuracy of the classi cation of the lifetime of each data pages [3]. Therefore, it is critical for any MS-SSD applications to precisely classify logical data pages according to their