Sector-Disk (SD) Erasure Codes for Mixed Failure Modes in RAID Systems

Abstract

Traditionally, when storage systems employ erasure codes, they are designed to tolerate the failures of entire disks. However, the most common types of failures are latent sector failures, which only affect individual disk sectors, and block failures which arise through wear on SSD's. This paper introduces SD codes, which are designed to tolerate combinations of disk and sector failures. As such, they consume far less storage resources than traditional erasure codes. We specify the codes with enough detail for the storage practitioner to employ them, discuss their practical properties, and detail an open-source implementation.

A Flash-aware Intra-disk Redundancy scheme for high reliable All Flash Array

“…However, these codes have to dedicate two or more drives to redundancy. To improve space efficiency, a series of strong erasure codes were developed to recover drive failures and sector faults simultaneously, such as PMDS codes in [7], SD codes in [8] and STAIR codes in [9]. However, these three codes have a significant update penalty and are only appropriate for storage systems that have limited updates.…”

“…The RAID-6 scheme is based on the array codes in [6]. The parameters of SD-codes in [8] are n ¼ 8, m ¼ 1, s ¼ 3, r ¼ 4. The ASPC scheme is the lifespan-aware adaptive SPC scheme and its stripe size changes from 256 to 8 [13].…”

Partial MDS (PMDS) and Sector-Disk (SD) codes that tolerate the erasure of two random sectors

“…Constructions of (1;2) SD codes were given in [1] and of (2;2) codes in [3]. These constructions are also summarized in [11] and the construction of (3;2) SD codes was verified for all r, n in GF(2 8 ) and for r, n 24 in GF(2 16 ). Hence, our results generalize those constructions.…”

“…Normally, these arrays are protected using the well known architectures known as Redundant Arrays of Independent Disks (RAID) [5]. Recent work has explored two types of erasure codes that extend RAID and are tailored for these scenarios: Partial-MDS (PMDS) codes and Sector-Disk (SD) codes [2], [3], [11], [12].…”

Binary random systematic erasure code for RAID system

“…However, it remains a hard work on large scale system. The newly proposed the sector-disk codes [14,15], and Stair code [16] still facing the hard problem of high computational complexity in Galois field.…”