Lifetime Of SSDs Research Articles

WA-Zone: Wear-Aware Zone Management Optimization for LSM-Tree on ZNS SSDs

ZNS SSDs divide the storage space into sequential-write zones, reducing costs of DRAM utilization, garbage collection, and over-provisioning. The sequential-write feature of zones is well-suited for LSM-based databases, where random writes are organized into sequential writes to improve performance. However, the current compaction mechanism of LSM-tree results in widely varying access frequencies (i.e., hotness) of data and thus incurs an extreme imbalance in the distribution of erasure counts across zones. The imbalance significantly limits the lifetime of SSDs. Moreover, the current zone-reset method involves a large number of unnecessary erase operations on unused blocks, further shortening the SSD lifetime. Considering the access pattern of LSM-tree, this article proposes a wear-aware zone-management technique, termed WA-Zone , to effectively balance inter- and intra-zone wear in ZNS SSDs. In WA-Zone, a wear-aware zone allocator is first proposed to dynamically allocate data with different hotness to zones with corresponding lifetimes, enabling an even distribution of the erasure counts across zones. Then, a partial-erase-based zone-reset method is presented to avoid unnecessary erase operations. Furthermore, because the novel zone-reset method might lead to an unbalanced distribution of erasure counts across blocks in a zone, a wear-aware block allocator is proposed. Experimental results based on the FEMU emulator demonstrate the proposed WA-Zone enhances the ZNS-SSD lifetime by 5.23×, compared with the baseline scheme.

CFIO: A conflict-free I/O mechanism to fully exploit internal parallelism for Open-Channel SSDs

I/O access conflicts make utilization within NVMe SSDs seriously low, which introduces unpredictable performance loss of NVMe SSDs. Although existing works adopt I/O isolation or conflict-aware I/O scheduling to avoid access conflicts, they can result in an unbalanced utilization and reduce the lifetime of NVMe SSDs. In this paper, we design and implement CFIO, a low-overhead conflict-aware I/O mechanism that achieves conflict-free I/Os to exploit the internal parallelism in NVMe SSDs. CFIO improves PU utilization and reduces I/O latency with two novel mechanisms. First, a conflict-free (CF) lane is proposed to eliminate conflicts by dividing I/O requests into conflict-free PU queues based on physical addresses. The PU queues correspond to the PU resources within the NVMe SSDs. Second, a k-RR scheduler is designed to dispatch reading and writing requests to NVMe SSDs in batches and separately. K-RR scheduler can fully exploit the internal parallelism of NVMe SSDs and form an I/O pipeline based on the dual registers of PU. Finally, we integrate CFIO into the LightNVM with Open-Channel NVMe SSD (OCSSD) and compare it with several existing solutions. Our evaluations show that CFIO improves the throughput of OCSSD by 19.32% and reduces its tail latency by 23.71%, compared to state-of-the-art methods.

RealWear: Improving performance and lifetime of SSDs using a NAND aging marker

Although NAND flash memory has revolutionized how we manage data in modern digital systems, significant improvements are needed in flash-based storage systems to meet the requirements of emerging data-intensive applications. In this paper, we address the problem of NAND aging markers that represent the wearing degree of NAND cells. Since all flash operations are affected by the wearing status of NAND cells, an accurate NAND aging marker is critical to develop flash optimization techniques. From our evaluation study, we first show that the existing P/E cycle-based aging marker (PeWear) is inadequate to estimate the actual aging status of NAND blocks, thus losing opportunities for further optimizations. To overcome the limitations of PeWear, we propose a new NAND aging marker, RealWear, based on extensive characterization studies using real 3D TLC flash chips. By considering multiple variables that can affect the NAND cell wear, RealWear can accurately indicate the actual wear status of NAND blocks during run time. Using three case studies, we demonstrate that RealWear is effective in enhancing the lifetime and performance of a flash storage system. Our experimental results showed that RealWear can extend the lifetime of individual NAND blocks by 63% and can reduce the GC overhead by 21%. Furthermore, RealWear significantly mitigates read latency fluctuations, guaranteeing that the read latency can be bounded with at most 2 read retry operations.

Efficient and Consistent NVMM Cache for SSD-Based File System

Buffer caching is an effective approach to improve the system performance and extend the lifetime of SSDs. However, the frequent synchronization operations in most real-world applications limit such advantages. This paper proposes to adopt emerging non-volatile main memories (NVMMs) to relieve the above problems while achieving both efficient and consistent cache management. To this end, an adaptive fine-grained cache (AFCM) scheme is proposed, which is motivated by our observation that the file data in many synchronized pages is partially updated for a wide range of workloads, implying that fine-grained cache management can save the NVMM cache space wasted by the clean parts. To reduce the cache index overhead introduced by fine-grained cache management, AFCM employs a Hybrid Cache based on DRAM and NVMM, with which the normal read and write operations are served without performance penalty. We also propose the Transactional Copy-on-Write mechanism to guarantee the crash consistency of both NVMM cache space and file system image. Our experimental results show that AFCM provides up to 84 percent performance improvement and 63 percent SSD write reduction on average compared to the conventional coarse-grained cache management scheme.

Isolation: Inexpensively separating cold data via garbage collection to improve the lifetime and performance of NAND flash SSDs

SummaryAn effective way to mitigate the lifetime and performance problems of NAND flash SSDs induced by garbage collection is separating the cold data and hot data. However, all existing solutions do this separation from the viewpoint of the hot data and thus suffer from expensive cost on monitoring the update behaviors of workloads. Different from the conventional wisdom, we propose to do the separation from the viewpoint of the cold data, which is rooted on the following two dedicated observations. First, the data migrated by garbage collection demonstrate a cold property compared with the other data. Second, it is inexpensive to separate the former data from the latter data. In the proposed method, named Isolation, we inexpensively separate the cold data via garbage collection. More specifically, through writing the data migrated by garbage collection (cold data) to dedicated blocks and writing the other data (hot data) to other blocks, the separation is done naturally. To evaluate Isolation, we conduct extensive trace‐driven simulations under seven typical workloads. The simulation results demonstrate the effectiveness and efficiency of Isolation. In most cases, Isolation can reduce the number of erasures and average I/O response time up to 47.3% and 80.1%, respectively. Existing approaches integrated with Isolation can further reduce the number of erasures and average I/O response time up to 7.8%‐18.5% and 10.7%‐41.4%, respectively.

Lifetime-aware FTL to improve the lifetime and performance of solid-state drives

Data compression techniques have been deployed in SSDs to prolong their lifetime due to the good tradeoff between data reduction and performance degradation. However, existing schemes either consume plenty of DRAM resources, or cause the read amplification problem, which may further result in significant performance degradation. In this paper, we propose a lifetime-aware FTL scheme (LAFTL) to improve both the lifetime and performance of SSDs by compressing several pages into one physical page. We then design a compression-aware page mapping table (PMT) to reduce the memory consumption, and propose a latency-aware approach to improve the performance. We conduct extensive trace-driven evaluations based on real-world workloads, and results show that our LAFTL reduces the average response time of reads by 3%–78% and ensures a minimal resource consumption in DRAM while obtaining an acceptable data reduction rate compared to other schemes.

Optimizing RAID/SSD controllers with lifetime extension for flash-based SSD array

Flash-based SSD RAID arrays are increasingly being deployed in data centers. Compared with HDD arrays, SSD arrays drastically enhance storage density and I/O performance, and reduce power and rack space. Nevertheless, SSDs suffer aging issues. Though prior studies have been conducted to address this disadvantage, effective techniques of RAID/SSD controllers are urgently needed to extend the lifetime of SSD arrays. In this paper, we for the first time apply approximate storage via the interplay of RAID and SSD controllers to optimize the lifespan of SSD arrays. Our basic idea is to reuse faulty blocks (those contain pages with uncorrectable errors) to store approximate data (which can tolerate more errors). By relaxing the integrity of flash blocks, we observed that the endurance of NAND flash memory can be significantly boosted, thereby providing huge potentials to significantly extend the lifetime of SSDs. Based on this observation, we propose the use of an efficient space management scheme for data allocation and FTL strategies by coordinating the interplay of RAID and SSD controllers to optimize the lifetime of SSD arrays. We implemented a prototype, called FreeRAID, based on an SSD array simulator. Our experiments show that we can significantly increase the lifetime by up to 2.17× compared with conventional SSD-based RAID arrays.

FineDedup: A Fine-grained Deduplication Technique for Extending Lifetime of Flash-based SSDs

FineDedup: A Fine-grained Deduplication Technique for Extending Lifetime of Flash-based SSDs

Slack Space Recycling: Delaying On-Demand Cleaning in LFS for Performance and Endurance

The Log-structured File System (LFS) transforms random writes to a huge sequential one to provide superior write performance on storage devices. However, LFS inherently suffers from overhead incurred by cleaning segments. Specifically, when file system utilization is high and the system is busy, write performance of LFS degenerates significantly due to high cleaning cost. Also, in the newer flash memory based SSD storage devices, cleaning leads to reduced SSD lifetime as it incurs more writes. In this paper, we propose an enhancement to the original LFS to alleviate the performance degeneration due to cleaning when the system is busy. The new scheme, which we call Slack Space Recycling (SSR), allows LFS to delay on-demand cleaning during busy hours such that cleaning may be done when the load is much lighter. Specifically, it writes modified data directly to invalid areas (slack space) of used segments instead of cleaning on-demand, pushing back cleaning for later. SSR also has the added benefit of increasing the lifetime of the now popular SSD storage devices. We implement the new SSR-LFS file system in Linux and perform a large set of experiments. The results of these experiments show that the SSR scheme significantly improves performance of LFS for a wide range of storage utilization settings and that the lifetime of SSDs is extended considerably.