The hard disk drive (HDD) market is set to shrink from $37 billion in 2012 to $33 billion in 2013 and $32 billion in ( Global shipments of solid-state drives are expected to more than double this year… Longer term, shipments are projected to reach 239 million units in 2016, comprising about 40% of the size of the market for hard-disk drives.

-same form factor -size and shape to fit platter - not much to see actually

Advantages No spin-up time Extremely low random access time (about 0.1ms) Consistent read time throughout the SSD (while on a HDD if the data is written in a fragmented way, read ops will have varying response times) Zero defragmentation No noise (great for a home NAS) Very light (SSDs size is 2,5" with SATA connectors) Lower power consumption (Excellent for the environment ) Unaffected by magnetic fields Very robust

Disadvantages Cost per GB Limited maximum capacity Limited P/E cycles Performance degradation Write amplification (Garbage collection, trim) Security issues (safe erase, cryptography)

AttributeSSD (Solid State Drive)HDD (Hard Disk Drive) Power Draw / Battery Life Less power draw, averages 2 – 3 watts, resulting in 30+ minute battery boost More power draw, averages 6 – 7 watts and therefore uses more battery Cost Expensive, $1.00 per gigabyte (based on buying a 240GB drive) Only around $0.075 per gigabyte, very cheap (buying a 4TB model) Capacity Typically not larger than 512GB for notebook size drives Typically 500GB – 2TB for notebook size drives Operating System Boot TimeAround 22 seconds average bootup timeAround 40 seconds average bootup time Noise There are no moving parts and as such no sound Audible clicks and spinning can be heard Vibration No vibration as there are no moving parts The spinning of the platters can sometimes result in vibration Heat Produced Lower power draw and no moving parts so little heat is produced HDD doesn’t produce much heat, but it will have a measurable amount more heat than an SSD due to moving parts and higher power draw Failure Rate Mean time between failure rate of 2.0 million hours Mean time between failure rate of 1.5 million hours File Copy / Write Speed Generally above 200 MB/s and up to 500 MB/s for cutting edge drives The range can be anywhere from 50 – 120MB / s File Opening SpeedUp to 30% faster than HDDSlower than SSD Magnetism Affected? An SSD is safe from any effects of magnetism Magnets can erase data

SSD components: Memory - Static RAM (SRAM battery powered) fastest (cache) - Dynamic RAM (DRAM battery powered) fast main ram - EEPROM (cancellazione totale) - Flash NOR (gates) NOR allows random-access for reading, Byte-Level access, slow replaces ROM, BIOS, Firmware - Flash NAND (gates) page/block access, cheap, fast SSD componetnts: Controller The controller is an embedded processor that executes firmware-level code and is one of the most important factors of SSD performance. Some of the functions performed by the controller include: Error correction (ECC) Wear leveling Bad block mapping Read scrubbing and read disturb management Read and write caching Garbage collection Encryption

Disadvantages: wite amplification Applcation file Create, update,... O.S. Filesystem CONTROLLER PHYSICAL BLOCKS

Writing is possible only to empty cells, no overwriting Writing is done at page level (4KB), erasing only at block level (128 pages = 512 KB)

Disadvantages, W.A.: Garbage collection GC is the name for the process of relocating existing data to new locations and allowing the surrounding invalid data to be erased. TRIM (O.S.) The TRIM command is designed to enable the operating system to notify the SSD of which pages of data are now invalid due to erases by the user or operating system itself. During a delete operation the OS will not only mark the sectors as free for new data, but it will also send a TRIM command to the SSD with the associated LBAs to be marked as no longer valid. After that point the SSD knows not to relocate the data from those LBAs during garbage collection. Wear Leveling limited P/E cycles Moving the data around to make sure each cell is evenly worn.

Attribute or characteristicSolid-state driveHard disk drive Start-up time Almost instantaneous; no mechanical components to prepare. May need a few milliseconds to come out of an automatic power-saving mode. Disk spin-up may take several seconds. A system with many drives may need to stagger spin-up to limit peak power drawn, which is briefly high when an HDD is first started. Access time As data can be retrieved directly from various locations of the flash memory, access time is usually not a big performance bottleneck. Typically under 100 µs. Much higher than SSDs. Read time is different for every different seek, since the location of the data on the disk and the location of the read-head make a difference. Ranges from 2.9 (high end server drive) to 12 ms (laptop HDD) due to the need to move the heads and wait for the data to rotate under the read/write head [80] [80] Data transfer rate SSD technology can deliver rather consistent read/write speed, but when lots of individual smaller blocks are accessed, performance is reduced. In consumer products the maximum transfer rate typically ranges from about 100 MB/s to 600 MB/s, depending on the disk. Enterprise market offers devices with multi-gigabyte per second throughput. Once the head is positioned, when reading or writing a continuous track, an enterprise HDD can transfer data at about 140 MB/s. In practice transfer speeds are many times lower due to constant seeking, as files are read from various locations or they are fragmented. Data transfer rate depends also upon rotational speed, which can range from 4,200 to 15,000 rpm. and also upon the track (reading from the outer tracks is faster due higher absolute head velocity relative to the disk). Fragmentation (Filesystem specific) There is limited benefit to reading data sequentially (beyond typical FS block sizes, say 4kB), making fragmentation negligible for SSDs. Defragmentation would cause wear by making additional writes of the NAND flash cells, which have a limited cycle life. Files, particularly large ones, on HDDs usually become fragmented over time if frequently written; periodic defragmentation is required to maintain optimum performance.

Noise (acoustic) SSDs have no moving parts and therefore are basically silent, although electric noise from the circuits may occur. HDDs have moving parts (heads, actuator, and spindle motor) and make some sound; noise levels vary between models, but can be significant (while often much lower than the sound from the cooling fans). Laptop hard disks are relatively quiet. Temperature control [ SSDs do not usually require any special cooling and can tolerate higher temperatures than HDDs. High temperatures can shorten the life of a hard disk, and reliability will be compromised. Fan cooling may be required if temperatures would otherwise exceed these values. Susceptibility to environmental factorsNo moving parts, very resistant to shock and vibration Heads floating above rapidly rotating platters are susceptible to shock and vibration Susceptibility to magnetic fieldsNo impact on flash memory Magnets or magnetic surges could in principle damage data, although the magnetic platters are usually well- shielded inside a metal case. Weight and size Solid state drives, essentially semiconductor memory devices mounted on a circuit board, are small and light in weight. However, for easy replacement, they often follow the same form factors as HDDs (3.5", 2.5" or 1.8"). Such form factors typically weigh as much as their HDD counterparts, mostly due to the enclosure. HDDs typically have the same form factor but may be heavier. This applies for 3.5" drives, which typically weigh around 700 grams. Reliability and lifetime SSDs have no moving parts to fail mechanically. Each block of a flash-based SSD can only be erased (and therefore written) a limited number of times before it fails. The controllers manage this limitation so that drives can last for many years under normal use. HDDs have moving parts, and are subject to potential mechanical failures from the resulting wear and tear. The storage medium itself (magnetic platter) does not essentially degrade from read and write operations.

Secure writing 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. However the drive's firmware may exchange damaged blocks with spare areas, so bits and pieces may still be present. Cost per capacityNAND flash SSDs have reached US$0.59 per GB HDDs cost about US$0.05 per GB for 3.5 inch and $0.10 per GB for 2.5 inch drives Storage capacity In 2011 SSDs were available in sizes up to 2 TB, but less costly 64 to 256 GB drives were more common. In 2011 HDDs of up to 4 TB were available. Read/write performance symmetry Less expensive SSDs typically have write speeds significantly lower than their read speeds. Higher performing SSDs have similar read and write speeds. 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 no longer in use can be reclaimed by TRIM; however, even with TRIM, fewer free blocks cause slower performance. HDDs are not affected by free blocks and do not benefit from TRIM Power consumption High performance flash-based SSDs generally require half to a third of the power of HDDs. High-performance DRAM SSDs generally require as much power as HDDs, and must be connected to power even when the rest of the system is shut down. The lowest-power HDDs (1.8" size) can use as little as 0.35 watts. 2.5" drives typically use 2 to 5 watts. The highest- performance 3.5" drives can use up to about 20 watts.