نحوه محاسبه IOPS
در این مطلب می خواهیم به نحوه ماسبه میانگین IOPS هارد دیسک بپردازیم چیزی که نیاز بسیاری از کاربران هارد دیسک ها و استوریج ها می باشد ولی این محاسبه کار آسانی نمی باشد.
How to calculate the average IOPS writen to disk? Good question but not always easy to answer.
Accoridng SNIA’s Dictionary the write penalty is inherent in RAID data protection techniques, which require multiple disk I/O requests for each application write request, and ranges from minimal (mirrored arrays) to substantial (RAID Levels 5 and 6). Many RAID array designs include features such as write-back cache specifically to minimize the write penalty.
WRITE PENALTY
RAID 5 (4+1) = 4
RAID 1 (1+1) = 2
RAID 10 (1+1) = 2
RAID 10 (2+2) = 2
RAID1
In a RAID1 environment the formula is:
h = disk IOPS / (r+2w)
h= 520 / 0.7+(2×0.3) = 520 / 0.7+0.6 = 520 / 1.3 = 400
In my case, with 4 x 180 IOPS, you have 720 disk IOPS available. To get host IOPS you need to know your read/write rate. If it is 60/40 read/write, it is
h = 720 /(0.6 + 2*0.4)
h = 512 IOPS
Note the above equation is derived from the equation for disk IOPS from host load (h = host IOPS, r = read%, w = write%) which for RAID 1 and RAID 1/0 is as follows:
r*h + 2*(w*h) = diskIOPS
example r = 60% and w = 40%, for 10000 host IOPS
.6*10000 + 2 * 0.4 * 10000= diskIOPS
6000 + 2 * 4000= diskIOPS
14000 = diskIOPS
http://www.yonahruss.com/architecture/raid-10-vs-raid-5-performance-cost-space-and-ha.html
http://sudrsn.wordpress.com/2010/12/25/iops-raid-penalty-and-workload-characterization/
In this example I use the following specs: