首先需要知道I/O中讀操作(Read)與寫操作(Write)所占的百分比。然後通過下列公式,将主機的IOPS需求轉換成硬碟實際IOPS負載:
RAID類型 公式
RAID 5和3 Drive IOPS = Read IOPS + 4*Write IOPS
RAID 6 Drive IOPS = Read IOPS + 6*Write IOPS
RAID 1和1/0 Drive IOPS = Read IOPS + 2*Write IOPS
假定4500 IOPS中讀/寫比是2:1,則不同RAID類型Drive IOPS要求分别如下:
RAID 10: (2/3)*4500 + 2*(1/3)*4500 = 6000 IOPS
RAID 5: (2/3)*4500 + 4*(1/3)*4500 = 9000 IOPS
RAID 6: (2/3)*4500 + 6*(1/3)*4500 = 12000 IOPS
再參照下表中不同類型硬碟單塊IOPS參數,得出需要多少塊硬碟:
硬碟類型 IOPS
Fibre Channel 15k rpm 180
SAS 15k rpm 180
Fibre Channel 10k rpm 140
SATA 7.2k rpm 80
SATA 5.4k rpm 40
Flash drive 2500
假定選用FC 15K RPM硬碟,則:
RAID 1/0: 6000/180 = 34 塊
RAID 5: 9000/180 = 50 塊
RAID 6: 12000/180 = 67 塊
注:實際情況下還需考慮Vault Drivers (共5塊)以及Hot Spares (建議每30塊硬碟一個)。