Comparing SSD Vs. HDD Input/Output Operation
The performance of a storage device can be quantified as the number of Input/Output operations Per Second (IOPS) it achieves. HDD IOPS is proportional to RPM. When a system requests to read/write data randomly from/to a HDD, seek time and rotational latency are two HDD activities that significantly reduce HDD IOPS. Seek time is the time it takes to move the HDD head to the correct cylinder to begin to receive data. Rotational latency is the time it takes to rotate the HDD platter beneath the head so that the data can be read/written. Rotational latency varies based on the RPM of the HDD.
NAND flash is used as the non-volatile memory inside SSDs. It has faster random read than random write performance, since its write performance is delayed by the need to perform garbage collection to free space for writing. However, since NAND flash has no moving parts, the SSD achieves much higher IOPS than a HDD.
For the client PC usage model with approximately a 50:50 read/write ratio, a PC IOPS number can be calculated as follows:
Using this equation, the results for client SSD PC performance are as follows:
- 2006/7 SSD Generation: 5,000 Read IOPS; 10 Write IOPS; 20 PC IOPS
- 2008 SSD Generation: 10,000 Read IOPS; 100 Write IOPS; 200 PC IOPS
- 2009 (estimated) SSD Generation: 25,000 Read IOPS; 400 Write IOPS; 785 PC IOPS
Read more about this topic: VRPM
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