缓存大小： T p o s i t i o n T_{position} Tposition代表写操作前旋转和寻道开销时间，磁盘传输速率 R p e a k R_{peak} RpeakMB/s，因此传输 D D DMB需要的时间 T w r i t e T_{write} Twrite
T w r i t e = T p o s i t i o n + D R p e a k T_{write} = T_{position} + \frac{D}{R_{peak}} Twrite=Tposition+RpeakD
写效率
R e f f e c t i v e = D T w r i t e = D T p o s i t i o n + D R p e a k R_{effective} = \frac{D}{T_{write}} = \frac{D}{T_{position} + \frac{D}{R_{peak}}} Reffective=TwriteD=Tposition+RpeakDD
写效率是以传输速率为基准，用F(0<F<1)表示
R e f f e c t i v e = D T p o s i t i o n + D R p e a k = F × R p e a k R_{effective} = \frac{D}{T_{position} + \frac{D}{R_{peak}}} = F \times R_{peak} Reffective=Tposition+RpeakDD=F×Rpeak
D = F × R p e a k × ( T p o s i t i o n + D R p e a k ) D = F \times R_{peak} \times (T_{position} + \frac{D}{R_{peak}}) D=F×Rpeak×(Tposition+RpeakD)
变换得到
D = F 1 − F × R p e a k × T p o s i t i o n D = \frac{F}{1-F} \times R_{peak} \times T_{position} D=1−FF×Rpeak×Tposition
假设要得到90%的效率，假设 T p o s i t i o n T_{position} Tposition为0.01秒，磁盘传输速率为100MB/s，因此计算D为9MB，因此缓存大小为9MB