Performance Comparison of SSD and HDD in Server RAID Configurations Using fio

SSD (Solid State Drive) advantages over traditional HDD (Hard Disk Drive) are well known for speed, prompting many servers to adopt SSDs; the author conducted a precise performance test to quantify how much faster SSD‑based servers are in both sequential and random I/O scenarios.

Test Environment : Two servers with RAID‑5 arrays were used. The HDD server employed a PERC H730 Mini RAID card with 1 GB cache and four 500 GB SSDs (typo in original, actually HDD configuration) totaling 1.3 TB usable. The SSD server used the same RAID card with seven 300 GB HDDs forming a RAID‑5 array with 1.6 TB usable.

fio Test Parameters : The asynchronous libaio engine was chosen, Direct I/O was enabled to bypass Linux page cache, testing was performed on files (not raw devices), each file was 100 GB (far larger than the RAID cache), and the noop scheduler was used.

Sequential Read Benchmark : Results (shown in the included images) indicate that under sequential I/O the HDD‑based RAID server does not fall far behind the SSD‑based one because the RAID controller’s prefetch and the inherent strength of sequential access for mechanical disks keep performance relatively high.

Random Read Benchmark : With page cache disabled and a 100 GB test file, the HDD’s random I/O performance was extremely poor, while the SSD achieved roughly 32 MB/s bandwidth (versus less than 1 MB/s for HDD) and about 120 µs latency (versus ~4.4 ms for HDD), representing a several‑tens‑fold improvement.

Conclusion : In server‑grade machines with RAID cache, sequential I/O performance of HDD RAID arrays remains acceptable, but for random I/O workloads SSDs provide dramatically higher throughput and lower latency. Therefore, when a server experiences heavy random I/O that exceeds page cache and RAID cache capacity, replacing HDDs with SSDs is strongly recommended.