Building Reliable Massive Capacity SSDs through a Flash Aware RAID-Like Protection

Abstract

The demand for mass storage devices has become an inevitable consequence of the explosive increase in data volume. The three-dimensional (3D) vertical NAND (V-NAND) and quad-level cell (QLC) technologies rapidly accelerate the capacity increase of flash memory based storage system, such as SSDs (Solid State Drives). Massive capacity SSDs adopt dozens or hundreds of flash memory chips in order to implement large capacity storage. However, employing such a large number of flash chips increases the error rate in SSDs. A RAID-like technique inside an SSD has been used in a variety of commercial products, along with various studies, in order to protect user data. With the advent of new types of massive storage devices, studies on the design of RAID-like protection techniques for such huge capacity SSDs are important and essential. In this paper, we propose a massive SSD-Aware Parity Logging (mSAPL) scheme that protects against n-failures at the same time in a stripe, where n is protection strength that is specified by the user. The proposed technique allows for us to choose the strength of protection for user data. We implemented mSAPL on a trace-based simulator and evaluated it with real-world I/O workload traces. In addition, we quantitatively analyze the error rates of a flash based SSD for different RAID-like configurations with analytic models. We show that mSAPL outperforms the state-of-the-art RAID-like technique in the performance and reliability.

Differentiated Protection and Hot/Cold-Aware Data Placement Policies through k-Means Clustering Analysis for 3D-NAND SSDs

“…To write data back to the page where it was written, the block containing the page must first be erased. This erase operation is slower than the page write operation, and the number of erase-after-write operations, also known as the P/E cycle, is limited by the flash memory's manufacturing technology [14]. Four technologies are widely used today: single-level cell (SLC), multi-level cell (MLC), triple-level cell (TLC), and quad-level cell (QLC).…”

“…So, specifies differentiated data protection strength for each cluster. The management methods of striping and partial stripe parity for partial data follow the recent efficient log structure writing schemes [12,14]. Differentiated protection policy should be similar to the efficient log write methods.…”

“…Figure 4 depicts six clusters classified by the k-means algorithm based on the characteristics of these 3D-NAND flash memories to apply differentiated data protection strength based on error rates. If numbering the clusters in order from top left to right, depending on the error rates, the stripe of the first cluster sets the parity to n, the stripe of 2, 3, and 6 clusters sets the parity to n − 1, and the stripe of 4 and 5 clusters sets the parity to n − 2 to apply the differentiated data protection strength [14]. Assuming n (by analyzing the error incidence analysis introduced in Section 4, the number of parity per stripe can be adjusted to achieve the desired reliability level) is 2, one stripe spans five flash memory chips.…”

“…The raw bit error rate (RBER) of flash memory increases exponentially with the P/E cycle period as follows. In this equation, x represents the P/E cycle of the block, and A and B are constant values depending on the type and process of the flash memory [14].…”

Advanced Data Mining of SSD Quality Based on FP-Growth Data Analysis

“…In addition, currently, the SSD in the industry still uses NAND flash memory. The development of R&D capability has enabled the change from the original single-level cell (SLC) and multi-level cell (MLC) to the mainstream trinary-level cell (TLC) and the next-generation qual-level cell (QLC) [6] so as to meet the market price requirements. The goals regarding the process improvement of NAND flash memory are to reduce the overall cost of the SSD and increase the storage capacity, but the limitation of the "program and erase" cycle (PE cycle) [7] on NAND flash memory means that no effective improvement can be achieved; thus, the durability of the SSD remains questionable.…”