what is bottleneck of disk IO operation?

Question

what is bottleneck of disk IO operation?

Answer 1

Disk operations are very slow relative to the speed of the devices requesting information from them ... namely the CPU. The CPU is often waiting far too long for information from a disk to get back to it and loaded into memory.

Major slow down factors in tradition hard disks (excludes SSD):

Seek time

Bus speed

Bus speed is also a bottleneck because multiple devices are competing for time on th bus and only one device can use it at a time ... so sometimes you are simply waiting while something on the south bridge is finishing up before it can resume transferring data from the hard disk into memory as well.

Answer 2

That pretty much depends on what you do.

• If you are doing sequential access (e.g. copying a large file) the disk's rotation speed matters most.
• If you are doing random access (e.g. copying many smaller files) the head's movement dictates overall speed.
• If you are doing too many tiny accesses (such as updating a large SVN repository on Windows) then it's the queue of disk operations in the OS (can be seen in the Resource Monitor).

Answer 3

The mechanical parts on a normal harddrive. An SSD increases speed significantly as it doesn't have any moving parts.

Answer 4

Access time, mostly on spinning (i.e. physical) disks. The actual sequential transfer rates are usually not the problem.