Comparison of SSD with hard disk drives

Making a comparison between SSDs and ordinary (spinning) HDDs is difficult. Traditional HDD benchmarks are focused on finding the performance aspects where they are weak, such as rotational latency time and seek time. As SSDs do not spin, or seek, they may show huge superiority in such tests. However, SSDs have challenges with mixed reads and writes, and their performance may degrade over time. SSD testing must start from the (in use) full disk, as the new and empty (fresh out of the box) disk may have much better write performance than it would show after only weeks of use.

Comparisons reflect typical characteristics, and may not hold for a specific device.

Attribute or characteristic	Solid-state drive	Hard disk drive
Spin-up time	Almost Instantaneous; nothing mechanical to "spin up". May need a few milliseconds to come out of an automatic power-saving mode.	May take several seconds. With a large number of drives, spin-up may need to be staggered to limit total power drawn.
Random access time	About 0.1 ms - many times faster than HDDs because data is accessed directly from the flash memory	Ranges from 5–10 ms due to the need to move the heads and wait for the data to rotate under the read/write head
Read latency time	Generally low because the data can be read directly from any location; In applications where hard disk seeks are the limiting factor, this results in faster boot and application launch times (see Amdahl's law).	Generally high since the mechanical components require additional time to get aligned
Consistent read performance	Read performance does not change based on where data is stored on an SSD	If data is written in a fragmented way, reading back the data will have varying response times
Defragmentation	SSDs do not benefit from defragmentation because there is little benefit to reading data sequentially (beyond typical FS block sizes) and any defragmentation process adds additional writes on the NAND flash that already have a limited cycle life.	HDDs may require defragmentation after continued operations or erasing and writing data, especially involving large files .
Acoustic levels	SSDs have no moving parts and make no sound	HDDs have moving parts (heads, spindle motor) and have varying levels of sound depending upon model
Mechanical reliability	A lack of moving parts virtually eliminates mechanical breakdowns	HDDs have many moving parts that are all subject to failure over time
Susceptibility to environmental factors	No flying heads or rotating platters to fail as a result of shock, altitude, or vibration	The flying heads and rotating platters are generally susceptible to shock, altitude, and vibration
Magnetic susceptibility	No impact on flash memory	Magnets or magnetic surges can alter data on the media
Weight and size	The weight of flash memory and the circuit board material are very light compared to HDDs	Higher performing HDDs require heavier components than laptop HDDs (which are light, but not as light as SSDs)
Parallel operation	Some flash controllers can have multiple flash chips reading and writing different data simultaneously	HDDs have multiple heads (one per platter) but they are connected, and share one positioning motor.
Write longevity	Solid state drives that use flash memory have a limited number of writes over the life of the drive. SSDs based on DRAM do not have a limited number of writes.	Magnetic media do not have a limited number of writes.
Software encryption limitations	NAND flash memory cannot be overwritten, but has to be rewritten to previously erased blocks. If a software encryption program encrypts data already on the SSD, the overwritten data is still unsecured, unencrypted, and accessible (drive-based hardware encryption does not have this problem). Also data cannot be securely erased by overwriting the original file without special "Secure Erase" procedures built into the drive.	HDDs can overwrite data directly on the drive in any particular sector.
Cost per capacity	As of February 2011[update], NAND flash SSDs cost about (US)$1.20–2.00 per GB	As of February 2011[update], HDDs cost about (US)$0.05/GB for 3.5 in and $0.10/GB for 2.5 in drives
Storage capacity	As of April 2011[update], SSDs come in different sizes up to 2TB but are typically not larger than 40-120GB, due to their high cost per GB.	As of April 2011[update], HDDs are typically 500GB-1TB but drives as large as 2 or 3 TB are also available.
Read/write performance symmetry	Less expensive SSDs typically have write speeds significantly lower than their read speeds. Higher performing SSDs have a balanced read and write speed.	HDDs generally have slightly lower write speeds than their read speeds.
Free block availability and TRIM	SSD write performance is significantly impacted by the availability of free, programmable blocks. Previously written data blocks that are no longer in use can be reclaimed by TRIM; however, even with TRIM, fewer free, programmable blocks translates into reduced performance.	HDDs are not affected by free blocks or the operation (or lack) of the TRIM command
Power consumption	High performance flash-based SSDs generally require 1/2 to 1/3 the power of HDDs; High performance DRAM SSDs generally require as much power as HDDs and consume power when the rest of the system is shut down.	High performance HDDs generally require between 12-18 watts; drives designed for notebook computers are typically 2 watts.

Read original 'http://en.wikipedia.org/wiki/Solid-state_drive'

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