Hybrid Storage Write Spike Absorption via SSD Cache Extension
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Solution Overview
Problem
Existing hybrid storage solutions experience performance degradation due to 'write spikes' that overwhelm slower HDD drives, leading to insufficient storage array performance, especially when parity RAID schemes require multiple writes and reads.
Innovation Solution
Assigning SSDs as 'tier-zero' and HDDs as 'tier-one' storage, with a write cache extension in SSDs to absorb random writes, migrating data based on access frequency, and using metadata to manage logical block addresses, thereby preventing write spikes from affecting HDD performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If hybrid storage arrays use HDDs for primary storage with SSD caching, then storage capacity and cost-effectiveness are improved, but write performance degrades during write spikes
Solution Approach 1:
The storage system is segmented into multiple tiers: tier-zero (SSD cache), tier-one (HDD storage), and a newly introduced tier-two (additional SSD capacity). This segmentation allows write operations to be distributed across different storage media based on their performance characteristics, with tier-two specifically designed to absorb write spikes before they reach the slower tier-one storage.
Solution Approach 2:
Tier-two SSDs act as an intermediary layer between the host system and tier-one HDD storage. Write spikes are absorbed and buffered in tier-two, which then gradually transfers data to tier-one at a sustainable rate. This intermediary prevents the write spikes from directly impacting the performance of the HDD-based tier-one storage.
2Reliability
If parity RAID schemes are implemented for redundancy, then data reliability is improved, but write operations require multiple reads and writes increasing complexity
Solution Approach 1:
The system performs preliminary actions by pre-calculating and storing parity information in tier-zero or tier-two storage before actual write operations to tier-one. When write spikes occur, the parity data is already prepared in faster storage, reducing the need for multiple read-write cycles to tier-one HDDs and simplifying the write operation complexity.
3Speed
If intelligent caching software moves frequently accessed data to SSD tier, then read performance is improved, but write spike absorption capability is reduced
Solution Approach 1:
Different portions of the storage system are assigned different qualities and functions: tier-zero is optimized for frequently accessed data with high-speed caching, while tier-two is specifically designed with larger capacity to absorb write spikes. This local quality differentiation allows the system to simultaneously optimize for both read performance and write spike absorption without compromising either function.
Data Source
AI summary
In an embodiment, a hybrid storage array one uses two or more storage device tiers provided by solid state drives (SSDs) and hard disk drives (HDDs). Random writes are collected and written to a write cache extension, such as a portion of the SSD storage tier. The write cache extension absorbs such accesses that would otherwise be written to HDD storage directly. Data structures are created in a cache memory local to an array controller representing the location on the write cache extension to which the writes were committed and a location in the storage system where they were originally intended to go. The write cache extension can be enabled all of the time, or only when the array controller write cache experiences certain operating conditions, such as when its utilization exceeds a predetermined amount. The approach improves the overall performance of the hybrid array.