vRPM, or virtual Revolutions Per Minute, was a term for a synthetic
measurement of performance introduced by
SanDisk
SanDisk is a brand for flash memory products, including memory cards and readers, USB flash drives, solid-state drives, and digital audio players, manufactured and marketed by Western Digital. The original company, SanDisk Corporation was acquir ...
for
solid state drive (SSD) storage devices inside client
PCs. vRPM was created to give users a metric to compare SSD performance to the
hard disk drive (HDD) and to other SSDs. The term is no longer used.
vRPM answers the question: "How fast would you have to spin a virtual HDD to achieve the performance of an SSD in a client PC?" It uses a language that users understand, RPM (
revolutions per minute
Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines.
Standards
ISO 80000-3:2019 defines a unit of rotation as the dimension ...
), that is a
''de facto'' industry standard to measure the performance of the HDD inside PCs.
Comparing SSD vs. HDD input/output operation
The performance of a storage device can be quantified as the number of
Input/Output
In computing, input/output (I/O, or informally io or IO) is the communication between an information processing system, such as a computer, and the outside world, possibly a human or another information processing system. Inputs are the signals ...
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 Higher performance in hard disk drives comes from devices which have better performance characteristics. These performance characteristics can be grouped into two categories: access time and data transfer time (or rate).
Access time
The ''access ...
and
rotational latency Higher performance in hard disk drives comes from devices which have better performance characteristics. These performance characteristics can be grouped into two categories: access time and data transfer time (or rate).
Access time
The ''access ...
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
A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base.
A cylinder may also be defined as an infin ...
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
Flash memory is an electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for the NOR and NAND logic gates. Both use ...
is used as the
non-volatile memory
Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data.
Non-volatile memory typi ...
inside SSDs. It has faster random read than random write performance, since its write performance is delayed by the need to perform
garbage collection
Waste collection is a part of the process of waste management. It is the transfer of solid waste from the point of use and disposal to the point of treatment or landfill. Waste collection also includes the curbside collection of recyclabl ...
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:
: