H13-624: HCIP-Storage V5.5

A high watermark that is set too high leaves insufficient cache-buffer space; burst I/O can therefore produce I/O fluctuations and higher latency, affecting write performance. A low watermark set too low causes dirty cached data to be flushed to disks too frequently, which degrades write performance rather than read performance. Huawei recommends a 20% low watermark and adequate spacing between the high and low watermarks.