The hard disk drive (HDD) market is set to shrink from $37 billion in
2012 to $33 billion in 2013 and $32 billion in 2014 . (http://www.nasdaq.com)
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.
http://thessdreview.com/
-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)
Attribute
Power Draw / Battery Life
Cost
Capacity
Operating System Boot Time
Noise
Vibration
Heat Produced
Failure Rate
File Copy / Write Speed
File Opening Speed
Magnetism Affected?
SSD (Solid State Drive)
Less power draw, averages 2 – 3 watts,
resulting in 30+ minute battery boost
HDD (Hard Disk Drive)
More power draw, averages 6 – 7 watts and
therefore uses more battery
Expensive, $1.00 per gigabyte (based on Only around $0.075 per gigabyte, very cheap
buying a 240GB drive)
(buying a 4TB model)
Typically not larger than 512GB for
notebook size drives
Typically 500GB – 2TB for notebook size drives
Around 22 seconds average bootup time Around 40 seconds average bootup time
There are no moving parts and as such
no sound
Audible clicks and spinning can be heard
No vibration as there are no moving
parts
The spinning of the platters can sometimes
result in vibration
HDD doesn’t produce much heat, but it will
Lower power draw and no moving parts have a measurable amount more heat than an
so little heat is produced
SSD due to moving parts and higher power
draw
Mean time between failure rate of 2.0
million hours
Mean time between failure rate of 1.5 million
hours
Generally above 200 MB/s and up to 500 The range can be anywhere from 50 – 120MB
MB/s for cutting edge drives
/s
Up to 30% faster than HDD
Slower than SSD
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
Applcation
file
Create,
update, ...
O.S.
Filesystem
CONTROLLER
Disadvantages: wite amplification
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 characteristic
Solid-state drive
Hard disk drive
Start-up time
Almost instantaneous; no mechanical components to prepare. Disk spin-up may take several seconds. A system with many
May need a few milliseconds to come out of an automatic
drives may need to stagger spin-up to limit peak power drawn,
power-saving mode.
which is briefly high when an HDD is first started.
Access time
Much higher than SSDs. Read time is different for every
different seek, since the location of the data on the disk and
As data can be retrieved directly from various locations of the
the location of the read-head make a difference. Ranges from
flash memory, access time is usually not a big performance
2.9 (high end server drive) to 12 ms (laptop HDD) due to the
bottleneck. Typically under 100 µs.
need to move the heads and wait for the data to rotate under
the read/write head[80]
Data transfer rate
Once the head is positioned, when reading or writing a
continuous track, an enterprise HDD can transfer data at
SSD technology can deliver rather consistent read/write
about 140 MB/s. In practice transfer speeds are many times
speed, but when lots of individual smaller blocks are accessed,
lower due to constant seeking, as files are read from various
performance is reduced. In consumer products the maximum
locations or they are fragmented. Data transfer rate depends
transfer rate typically ranges from about 100 MB/s to
also upon rotational speed, which can range from 4,200 to
600 MB/s, depending on the disk. Enterprise market offers
15,000 rpm. and also upon the track (reading from the outer
devices with multi-gigabyte per second throughput.
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)
HDDs have moving parts (heads, actuator, and spindle
motor) and make some sound; noise levels vary between
SSDs have no moving parts and therefore are basically
models, but can be significant (while often much lower
silent, although electric noise from the circuits may occur.
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 factors
No moving parts, very resistant to shock and vibration
Heads floating above rapidly rotating platters are
susceptible to shock and vibration
No impact on flash memory
Magnets or magnetic surges could in principle damage
data, although the magnetic platters are usually wellshielded inside a metal case.
Susceptibility to magnetic fields
Weight and size
Solid state drives, essentially semiconductor memory
devices mounted on a circuit board, are small and light in
HDDs typically have the same form factor but may be
weight. However, for easy replacement, they often follow
heavier. This applies for 3.5" drives, which typically weigh
the same form factors as HDDs (3.5", 2.5" or 1.8"). Such
around 700 grams.
form factors typically weigh as much as their HDD
counterparts, mostly due to the enclosure.
Reliability and lifetime
SSDs have no moving parts to fail mechanically. Each block
HDDs have moving parts, and are subject to potential
of a flash-based SSD can only be erased (and therefore
mechanical failures from the resulting wear and tear. The
written) a limited number of times before it fails. The
storage medium itself (magnetic platter) does not
controllers manage this limitation so that drives can last
essentially degrade from read and write operations.
for many years under normal use.
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 (drivebased 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 capacity
NAND 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
In 2011 HDDs of up to 4 TB were available.
64 to 256 GB drives were more common.
Secure writing limitations
Read/write performance symmetry
Free block availability and TRIM
Less expensive SSDs typically have write speeds significantly
lower than their read speeds. Higher performing SSDs have
similar read and write speeds.
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
HDDs generally have slightly lower write speeds than their
read speeds.
HDDs are not affected by free blocks and do not benefit from
TRIM
performance.
Power consumption
High performance flash-based SSDs generally require half to a
third of the power of HDDs. High-performance DRAM SSDs
The lowest-power HDDs (1.8" size) can use as little as 0.35
generally require as much power as HDDs, and must be
watts. 2.5" drives typically use 2 to 5 watts. The highestconnected to power even when the rest of the system is shut performance 3.5" drives can use up to about 20 watts.
down.