Solid State Drives

If a solid-state drive doesn’t have any moving parts, how does it store data?

Instead of using motors and magnets, they use electrical current to signify the 1s and 0s that all data is comprised of.

While a magnetic hard drive works by changing the magnetism of sectors on a spinning platter, solid-state drives have lots and lots of tiny transistors.
When an electrical current is able to pass through a transistor it represents a 1, and a 0 is represented when a transistor does not accept current. 
Every solid-state drive has a controller. This is a processor that is responsible for reading and writing to the transistors and passing this data to the rest of the computer system to be used.
It also manages all the data on the drive, keeping track of where data is stored and making sure that data is distributed over the transistors evenly.
Cells are grouped into pages, which are usually 4KB. This is the smallest level of data that can be written to a SSD.
Similarly, pages are grouped into blocks, which are typically made up of 128 pages (512KB).
Taking it one step further, blocks are organized in groups of 1024 to form planes, which are usually 512MB in size.
Multiple planes make up one of the flash chips you can see on an SSD circuit board.

Advantages: 

1.    Speed:
This is the biggest reason to go for an SSD; they’re much, much faster than conventional hard drives in two different ways.
First of all, because there are no moving parts there is no wait. While the drive spins up or for a head to move to the
correct place to start reading the data there is very little waiting time, or latency.
Since data can be read from anywhere in the drive pretty much instantly, tasks which rely on lots of data being read from all over the place are completed much, much faster.

2.    Defrag: added benefit us that you never have to defragment your files, which is always a nice perk.

3.    outperforming HDDs in random reads, SSDs also have the upper hand in sustained reading and writing. 
 A typical new magnetic hard drive will be able to read at 60-80 MB/s, whereas a midrange solid-state drive will be able to read at anywhere from 175-250 MB/s.

 4.    Durability:
The other major advantage that SSDs have is again due to their lack of moving Parts, making it virtually invulnerable to vibrations, magnetism
or being dropped things that would seriously damage a magnetic drive.

5.    Noise:
Hard drives make a surprising amount of noise. Having a drive that completely outperforms a conventional hard drive while making no noise at all is a definite plus.

6.    Power Consumption:
One of the big things that defines a laptop is its battery life.
most solid-state drives draw a third to a half less power than even “low power” hard drives.

7.    Temperature:
hard drives get hot when they’re in use for long periods of time.
Rotating platters 7200 times a minute isn’t exactly the best way to keep a motor cool.
SSDs, on the other hand, generate very little heat and require no cooling

 Disadvantages

  1.       Price:
unfortunately SSDs are still very much a developing market, so you still pay a massive premium for all those advantages.

2.       Reliability/Longevity:

The major problem SSDs have is with longevity. As fast as the technology allows solid-state drives to be, it limits them in that each transistor may only be written to a
certain number of times before it becomes “stuck” and cannot be written to any more.
While the SSD‟s controller helps to handle this by distributing writing between the transistors with wear levelling,
eventually the drive will start to become very unreliable very quickly.

     3.       Long Term Performance:

over time the drive becomes full of data. While this doesn’t stop you from continuing to add data to the drive until you have filled the capacity of the drive, over time the writing speed of the drive appears to become slower and slower.
Put simply, this is because as the drive’s pages are all filled it needs to rearrange data to free more pages to write to.
there are now ways to alleviate the degradation without wiping the drive, usually involving either a command called TRIM or by the controller automatically carrying out a process called garbage removal in blocks that aren’t being used.

     4.       Data Recovery:

Usually it takes a long time for HDD hard drive to fail, giving you plenty of warning and the opportunity to back up the data to another source.
You don’t get that with a solid-state drive; when a drive fails, it fails completely and instantly.
when that happens, it’s impossible to retrieve the data.

     5.       Capacity: (compared to SATA and SAS 10KRPM disks)

 
     6.       Brands:
 be wary about buying a drive that is significantly cheaper than all the other SSDs with similar capacities. There’s usually a very good reason for it!

To be aware of:

      1.       Controllers:

The controller manages the data on the solid-state drive and keeps track of where the data is kept.
It’s very important to have a decent controller or the performance of the drive is seriously impaired
possible avoid SSDs based on a JMicron controller. The main ones you’ll want to get will use either the Indilinx “Barefoot” or SandForce controllers.
Intel and Samsung also make their own SSD controllers that perform well, too.

    2.       TRIM Support:

TRIM support is extremely important when it comes to buying an SSD
TRIM is a command which can be utilized by the Operating System to tell the SSD that it has deleted files and gives it the chance to free up pages that
aren’t being used any more by rewriting the block when it’s not in use.
This means that the block doesn’t need to be rewritten while you’re trying to write to it, which is what causes the performance degradation in the first place.

MLC vs. SLC:

It’s quite simple: MLC stands for multi-level cell, whereas SLC stands for single-level cell.
This means that each transistor (or cell) in an MLC drive holds two bits of information, whereas in an SLC they only hold one.
When checking for data, an SLC drive only needs to check if the bit is a 1 or a 0. On
the other hand, each cell in an MLC drive has four states: 11, 10, 01 or 00. This process takes around 3 times longer to perform.
The result is that an SLC has faster transfer speeds, lower power consumption and
has more read-write cycles, but has half of the storage density of an MLC drive for the same number of transistors,
making it much more expensive for a drive with the same capacity.
This makes them prohibitively expensive for consumer use, but perfect for enterprise servers that need the extra performance and reliability.

IT departments considering SSDs should take both the performance and the price/performance ratios into consideration before making a choice.

For some IT operations, the additional cost might not justify the performance improvement:

This technical report provides price vs. performance results:

http://www.dell.com/downloads/global/products/pvaul/en/ssd_vs_hdd_price_and_performance_study.pdf

The objective is to provide recommendations on drive types that are best suited for some common applications.

Since I guess you don’t have the time to read this long (but very interesting) report, I will write the bottom lines:

1.       for sequential access workloads, such as media streaming applications and SQL logs, the price/MBPS ratio is much greater than the corresponding performance ratio when moving from HDDs to SSDs.
2.       SSDs are best suited for applications that use random data accesses and small payload sizes.
Drive Recommendations for Each Application Workload I/O Profile: