磁盘寻道时间测量方法
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【中文标题】磁盘寻道时间测量方法【英文标题】：Disk seek time measurement method 【发布时间】：2016-11-12 12:32:50 【问题描述】：我编写了一个脚本来测量 HDD 上的寻道时间，并对其完成方式的微小变化导致显着不同的时间。
第一个循环在磁盘开头的区域内进行跳转。第二个周期选择磁盘上执行查找的随机区域（相同大小）。 这种方法明显不同，但我不明白为什么它会改变结果？请注意，对于大面积的测量，两种方法都会收敛。
Bytes* 方法只是很好地格式化数字 (1024 "1KB")。脚本必须在 root 下运行。磁盘默认为 sdb。
import sys, os, time, random
#--------------------------------------------------------------------------------------------------
def BytesString(n):
suffixes = ['B','KB','MB','GB','TB','PB','EB','ZB','YB']
suffix = 0
while n % 1024 == 0 and suffix+1 < len(suffixes):
suffix += 1
n /= 1024
return '01'.format(n, suffixes[suffix])
def BytesInt(s):
if all(c in '0123456789' for c in s):
return int(s)
suffixes = ['B','KB','MB','GB','TB','PB','EB','ZB','YB']
for power,suffix in reversed(list(enumerate(suffixes))):
if s.endswith(suffix):
return int(s.rstrip(suffix))*1024**power
raise ValueError('BytesInt requires proper suffix ('+' '.join(suffixes)+').')
def BytesStringFloat(n):
x = float(n)
suffixes = ['B','KB','MB','GB','TB','PB','EB','ZB','YB']
suffix = 0
while x > 1024.0 and suffix+1 < len(suffixes):
suffix += 1
x /= 1024.0
return '0:0.2f1'.format(x, suffixes[suffix])
#--------------------------------------------------------------------------------------------------
disk = open('/dev/sdb', 'r')
disk.seek(0,2)
disksize = disk.tell()
os.system('echo noop | sudo tee /sys/block/sdb/queue/scheduler > /dev/null')
print 'Syntax: progam [-s -sr -t -tr] [-v]: to run specific modes; for verbose mode.'
print 'Disk name: 0 Disk size: 1 Scheduler disabled.'.format(
disk.name, BytesStringFloat(disksize))
displaytimes = '-v' in sys.argv
#--------------------------------------------------------------------------------------------------
bufsize = 512
bufcount = 100
displaysamplecount = 24
for randomareas in [False,True]:
print
print 'Measuring: Random seek time 0'.format(
'using random areas of disk.' if randomareas else 'using beginning of disk.')
print 'Samples: 01 Sample size: 2'.format(
bufcount, ' (displayed 0)'.format(displaysamplecount) if displaytimes else '', bufsize)
for area in [BytesInt('1MB')*2**i for i in range(0,64)]+[disksize]:
if area > disksize:
continue
os.system('echo 3 | sudo tee /proc/sys/vm/drop_caches > /dev/null')
times = []
disk.seek(0)
disk.read(bufsize)
for _ in range(bufcount):
left = random.randint(0, disksize-area) if randomareas else 0
right = left + random.randint(0, area)
disk.seek(left)
disk.read(bufsize)
start = time.time()
disk.seek(right)
disk.read(bufsize)
finish = time.time()
times.append(finish-start)
times = sorted(times)[:bufcount*95/100]
print 'Area tested: 0:6 Average: 1:5.2f ms Max: 2:5.2f ms Total: 3:0.2f sec'.format(
BytesString(area) if area < disksize else BytesStringFloat(area),
sum(times)/len(times)*1000, max(times)*1000, sum(times))
if displaytimes:
print 'Read times: 0 ... 1 ms'.format(
' '.join(['0:0.2f'.format(x*1000) for x in times[:displaysamplecount/2]]),
' '.join(['0:0.2f'.format(x*1000) for x in times[-displaysamplecount/2:]]))
Measuring: Random seek time using beginning of disk.
Samples: 100 Sample size: 512
Area tested: 1MB Average: 0.14 ms Max: 0.35 ms Total: 0.01 sec
Area tested: 2MB Average: 0.16 ms Max: 0.31 ms Total: 0.02 sec
Area tested: 4MB Average: 0.20 ms Max: 0.75 ms Total: 0.02 sec
Area tested: 8MB Average: 0.19 ms Max: 0.97 ms Total: 0.02 sec
Area tested: 16MB Average: 0.64 ms Max: 7.97 ms Total: 0.06 sec
Area tested: 32MB Average: 2.29 ms Max: 10.56 ms Total: 0.22 sec
Area tested: 64MB Average: 3.89 ms Max: 12.25 ms Total: 0.37 sec
Area tested: 128MB Average: 6.32 ms Max: 13.18 ms Total: 0.60 sec
Area tested: 256MB Average: 6.73 ms Max: 13.04 ms Total: 0.64 sec
Area tested: 512MB Average: 7.43 ms Max: 13.72 ms Total: 0.71 sec
Area tested: 1GB Average: 8.38 ms Max: 13.59 ms Total: 0.80 sec
Area tested: 2GB Average: 8.51 ms Max: 13.81 ms Total: 0.81 sec
Area tested: 4GB Average: 8.87 ms Max: 13.86 ms Total: 0.84 sec
Area tested: 8GB Average: 9.82 ms Max: 14.66 ms Total: 0.93 sec
Area tested: 16GB Average: 9.73 ms Max: 15.95 ms Total: 0.92 sec
Area tested: 32GB Average: 9.89 ms Max: 15.18 ms Total: 0.94 sec
Area tested: 64GB Average: 10.60 ms Max: 15.85 ms Total: 1.01 sec
Area tested: 128GB Average: 11.18 ms Max: 18.68 ms Total: 1.06 sec
Area tested: 256GB Average: 13.31 ms Max: 30.94 ms Total: 1.26 sec
Area tested: 512GB Average: 14.14 ms Max: 31.70 ms Total: 1.34 sec
Area tested: 1TB Average: 15.20 ms Max: 33.35 ms Total: 1.44 sec
Area tested: 1.36TB Average: 15.47 ms Max: 25.30 ms Total: 1.47 sec
Measuring: Random seek time using random areas of disk.
Samples: 100 Sample size: 512
Area tested: 1MB Average: 7.21 ms Max: 35.94 ms Total: 0.69 sec
Area tested: 2MB Average: 5.40 ms Max: 12.92 ms Total: 0.51 sec
Area tested: 4MB Average: 6.97 ms Max: 36.60 ms Total: 0.66 sec
Area tested: 8MB Average: 7.24 ms Max: 15.05 ms Total: 0.69 sec
Area tested: 16MB Average: 7.36 ms Max: 13.03 ms Total: 0.70 sec
Area tested: 32MB Average: 7.34 ms Max: 12.30 ms Total: 0.70 sec
Area tested: 64MB Average: 7.35 ms Max: 13.47 ms Total: 0.70 sec
Area tested: 128MB Average: 7.66 ms Max: 13.37 ms Total: 0.73 sec
Area tested: 256MB Average: 7.93 ms Max: 13.34 ms Total: 0.75 sec
Area tested: 512MB Average: 10.16 ms Max: 39.67 ms Total: 0.97 sec
Area tested: 1GB Average: 8.76 ms Max: 14.38 ms Total: 0.83 sec
Area tested: 2GB Average: 9.42 ms Max: 17.74 ms Total: 0.89 sec
Area tested: 4GB Average: 11.00 ms Max: 23.22 ms Total: 1.05 sec
Area tested: 8GB Average: 10.59 ms Max: 19.60 ms Total: 1.01 sec
Area tested: 16GB Average: 10.91 ms Max: 19.15 ms Total: 1.04 sec
Area tested: 32GB Average: 11.19 ms Max: 26.02 ms Total: 1.06 sec
Area tested: 64GB Average: 12.59 ms Max: 26.49 ms Total: 1.20 sec
Area tested: 128GB Average: 11.97 ms Max: 19.30 ms Total: 1.14 sec
Area tested: 256GB Average: 12.61 ms Max: 22.84 ms Total: 1.20 sec
Area tested: 512GB Average: 13.62 ms Max: 20.48 ms Total: 1.29 sec
Area tested: 1TB Average: 16.72 ms Max: 29.20 ms Total: 1.59 sec
Area tested: 1.36TB Average: 15.96 ms Max: 26.21 ms Total: 1.52 sec
【问题讨论】：
【参考方案1】：现代 HDD 具有内置缓存 - 如果您读取某个位置，“某些逻辑”将在内部缓存它周围的区域，如果您下次读取它附近的内容，它将从缓存中提供数据（如果存在），否则从磁盘读取。
从磁盘的开头读取
Measuring: Random seek time using beginning of disk.
Samples: 100 Sample size: 512
Area tested: 1MB Average: 0.14 ms Max: 0.35 ms Total: 0.01 sec
将从那里缓存东西 - 连续读取将从（更快的）缓存中读取。
读取随机位置：
Measuring: Random seek time using random areas of disk.
Samples: 100 Sample size: 512
Area tested: 1MB Average: 7.21 ms Max: 35.94 ms Total: 0.69 sec
将无法从缓存中读取 - 除非您多次读取“相同的随机位置”。
你的代码没有使用 same 随机区域 100 次：
for _ in range(bufcount): left = random.randint(0, disksize-area) if randomareas else 0 right = left + random.randint(0, area) disk.seek(left) disk.read(bufsize) start = time.time() disk.seek(right) disk.read(bufsize) finish = time.time() times.append(finish-start)
它会为 100 个 bufcounts 中的每一个创建新的 left 和 right - 如果您是随机搜索，那么您不会从 HDD 缓存中获利（大多数情况下，除非随机命中类似的数字纯粹是偶然的）。
【讨论】：
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