But earlier generations of SSD had some issues with lifespan.
This key in of storage has limited life due to the physical properties of semiconductors.
But the industry pushed ahead, finding technical solutions to handle the issue.
Costs were also driven down, as the price of SSD was at first prohibitive.
They do not have to worry about how long their system will last.
SSDs and HDDs now both have a similar expected lifespan.
Here we explain the technical details of that so that you could judge for yourself.
SSD technology overview
Dr. An Wang invented the magnetic disk (non-volatile memory) in 1955.
It was a technological breakthrough.
He licensed it to IBM for their mainframes.
HDD replaced paper punch cards.
But the speed of magnetic HDDs have an inherent limit determined by the disk controller.
Engineers working at Bell Laboratories left there in 1957 to start what became Intel.
They took the transistor and created the semiconductor.
This, like Wangs magnetic disks, retained its information when powered off.
However, it was much more compact, enabling much faster speeds in opening or closing a circuit.
Semiconductors were engineered into CPUs to power computers.
But engineers realized that semiconductors too could function as storage if only they did not cost so much.
In theory you could store more on them than just programs.
Its physical properties are such that each die can handle about 100,000 writes before it wears out.
Multiple-level memory cells (MLC) increase the storage capacity over single level cells (SLC).
The expected lifespan of an MLC cell is 10,000 writes.
Hard disks and solid storage drives use this punch in of error correction code.
So does any kind of data transmission, including radios and TV transmission.
This ensures reliability as they transfer data.
For a data file, this is a checksum or MD5 hash (signature).
For disk drives, it is a parity bit or bits.
Disk drives calculate parity bits as they write data.
They say that NAND flash memory has a finite life expectancy and a naturally occurring error rate.
This is because of the physical properties of semiconductors.
If the result does not match the data, that block is marked as bad.
RAID and other replication schemes are then used to retrieve the correct data from a backup location.
The principles of ECC are the same for HDD and SDD.
Reliability of SSDs over time
What can we say about the reliability of SSD today?
Five years ago, the technology was not as common as today, because it cost too much.
Tech writers then were writing articles with headlines like How SSDs can hose your data.
This was the reviewers intimating that such devices were undependable.
At that time, flash drives were also thought to be incapable of sustaining repeat power outages.
So what has changed since then to improve the reliability of SDD?
The key thing is that there have been improvements to error correction codes.
Furthermore, better capacitors have been introduced to store information in volatile memory.
They all operate with pretty much the same physical characteristics.
PC or enterprise).
But first, Samsung has addressed the issue of memory fatigue.
It says the SM843T Data Center Series has extreme write endurance.
To address the power-failure issue, their drive includes tantalum capacitors.
Tantalum capacitors are more expensive than regular capacitors.
A capacitor holds an electric charge over a short period of time when its electricity is off.
Samsung says their SM843 drive has an UBER of 1 per 10^17 or 10E-7.
That number decreases in a linear fashion over time.
This means the BER of memory cells increases over time in a linear (i.e.
steady and predictable) manner.
The ECC algorithm built into the controller knows this.
As such it changes its data dispersal algorithm over time to ensure reliable operations.
Samsung says that the SM843 drive has a two million hour mean time before failure (MTBF).
This does not mean that the rig will last two million hours.
The number is a function of the bit error write times.
This is the greatest throughput (write speed) at which the equipment will operate.
Seagate, in a surprising statement, says that manufacturers are overreaching.
Presumably they are not talking about themselves.
Below we cite some test observations and warranty data from different manufacturers.
None of the tests show poor results, except perhaps the Samsung 840.
It uses triple-bit dies instead of a double-bit.
We would hope that is not the case for the average data center.
Lets look at some facts.
But this would be difficult.
The swappable nature of these devices that lets you replace failed components with new ones in a disk array.
Perhaps a reliable way to estimate SDD lifespan would be to look at the manufacturers warranty.
Below are some hard numbers on that.
Violins CEO makes the point that their SDDs match the 3 to 5 year depreciation schedule of HDDs.
So they should have a comparable lifespan.
(Depreciation is an accounting system used in the USA.
The table below shows the SDD model.
The columns show whether the model design is for the enterprise or mid-level market.
They also show the warranty in years, if available.
Finally, they comment on the technology used to ensure data integrity and recoverability.
This is a low-priced drive suitable for consumer laptops.
Samsung offered 1,000 guaranteed write operations on triple memory cells.
But in actual practice they supported three times as much.
Hardware.info also unplugged the power at certain intervals, and left the power off.
This tested whether memory cells might lose data after 1,000 operations.
They found there to be no problem with that.
The first uncorrectable write errors occurred after 3,000 operations.
At 4,000 operations they said that the drive was clinically dead, as write errors reached 58,000.
How long a drive lasts is also related to how much you use it.
That was the point of another study, which sought to wear out the devices faster.
They completed more operations in a shorter time than one would in practice.
This study, by the Tech Report, was also geared toward consumer, PC grade hardware.
These are all based on two-bit MLC flash.
They also tested the Samsung 840 Series 250G, which has a 3 bit TLC flash.
At that time, Samsung started reallocating sectors in a linear fashion.
These increased with usage, as shown in the graph below.
The graph shows it wearing out over time, unlike the other models.
They have not yet documented those results.
Conclusion
Given the information outlined above, we can see that SSDs are reliable for enterprise applications.
Their main use, however, is in cell phones and tablets.
For example, this is what iPads and iPhones use.
Users can copy their operating system to it, to make their computer run faster.
So get out your pen and paper.
Then call your salesman for a quote.
(Prices for hardware, electricity, negotiated discounts, and facilities rental vary between locations.)
SSD uses less electricity and reduces floor space.
This further reduces electricity costs for air conditioning.
If the cost is more or less the same, use SSD.
SSD is much faster than HDD.
This means it will boost customer satisfaction due to the increased performance of apps and websites.
On the reliability issue, that is a more complex question.
Much of the negative literature on the internet relates to laptops SSDs.
The literature does not relate to commercial-grade equipment.
The technology is in fact better than those critics say, as testing reveals.
Wear leveling has extended the life of memory cells.
High capacity capacitors have reduced the risk of power loss due to a power failure.
So the point about endurance turns out to be a moot one.
