average seek time 12ms
rotation rate 3600RPM
transfer rate 3.5MB/second
#sectors per track 64
sector size 512bytes
controller overhead 5.5ms
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suppose we have an array of 4 of these disks. they are all synchronized such
thtat the arms on all the disks are always on the same sector within the track
the data is striped across the 4 disk so that 4 logically consecutive sector
can be read in parallel. what is the average time to read 32 consecutive KB
from the disk array?
============================
since 4 logically consecutive secotrs can be read at once, we can read off 2KB
at once. to read 32KB, we need to read 16 sectors on each disk.
so, the time taken is the same as in (2)
(2) 12 + (0.5*60/3600) + (8*1024/(3.5*2^20)) + 5.5
請問為什麼是這樣算?
張凡335頁
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