Solid State Drives (SSD)

As an avid computer user I spend a lot of time using computers and being an electronic engineer it’s even expected of me. And it occurred to me that in my life I will use a lot of energy using computers and surly there’s someway to reduce this. I did some research and found out about alternatives to common computer components, and the one that intrigued me the most was solid state drives instead of hard drives.

The actual definition of solid-state refers to the use of semiconductor devices rather than electron tubes, but has been adopted as a term for this more modern technology.
SSDs don’t have any moving parts, they are instead made up of NAND flash (non-volatile) memory or SDRAM (volatile) memory. Because it has no moving parts it uses roughly half the energy that HDDs use.

Advantages:

• Faster start-up as no spin up is needed
• Faster random I/O
• Much faster seek times for read and write tasks
• In some cases longer lifetime
• Lower heat and noise production
• Better mechanical reliability – no moving parts removes most risks
• Can endure extreme shock, high altitude, vibration and temperatures
• Relatively deterministic performance – because fragmentation has less impact.
• Lower weight and size.

Disadvantages

• Very costly
• Limited capacity compared to moving part drives but the gap is closing rapidly (BiTMICRO Networks announced the release of SSD drives with capacities of up to 832GB, for release in Q3 2008.)
• Vulnerable to power loss, magnetic fields and electric/static charges.
• Slow random write drives
• Some SSDs have substantially lower throughput than conventional hard disks which can lead to lower performance.

Alternatives

Hard Disk Drive (HDD)

Hard disk drives work by having non volatile magnetic disks called platters that spin at high speeds. An arm with a read/write head on the end hovers over the surface of the platter, moving to where it’s needed. The head can magnetically write on the platter along tracks and also read the magnetic data from these tracks.

Advantages:

• Cheap as chips (in comparison)
• Larger capacity than SDDs (currently)
• Their faraday cages mean they are resistant to magnetic fields and electric/static charges

Disadvantages:

• Slower than SDD’s(both start up and read write functions)
• Uses about twice as much power
• Greater heat and noise generation
• Less mechanically reliable – more mechanical parts increase chance of faults
• Fragmentation has larger effect on there performance
• Heavier and larger.

Hybrid

Hybrid hard drives or HHDs are effectively HDDs but with one major difference, they have a large buffer of non-volatile flash memory to cache data during normal use.
In normal HDDs the platters spin all the time but because the HHDs primarily use the large buffer for non-volatile data storage, the platters are at rest most of the time.
During these times the information that would usually be written to the hard drive is saved to the buffer instead. For example when working on a text document or browsing the web any temporary save files or the browser's disk cache would normally be written to the hard drive is instead saved to buffer. There’s only two situations when the hard drives platter spins up, firstly when the buffer nears its maximum capacity, the platters spin up and all the data in the buffer is cleared to the hard drive so that the buffer is empty again for further use and after this the platter returns to its state of rest. The second is when the user needs to access data not already stored on the buffer in which case the platters spin up just long enough to transfer the needed file over to the buffer before going back to rest.

Advantages

• Decreased power consumption compared to HDD: since the platters won’t be spinning most of the time power the power usually used to spin them constantly will be saved. In the case of desktop computers this will actually increase system performance significantly, reduce boot time and enable instant startup from sleep and hibernation. As for mobile computers it will greatly increase the system runtime while running on battery.
• Reduced heat production: because the platters are spinning less, less friction is created by the moving parts and so less heat is generated.
• Lower noise levels: due to the reduction in power consumption and heat production a HHD needs less cooling, meaning less noise. HHDs are almost completely silent under normal circumstances due to the decreased usage of the platters.
• Better reliability: Hybrid drives should last longer than standard hard drives as they are submitted to less wear and tear because its moving parts are stationary most of the time. Also there are less head crashes (when a sudden movement causes the read/write head of the hard drives arm to physically impact on the platter) as most of the moving parts are stationary most of the time.
• Improved performance: this is because of the filesystem format can be kept together on the flash buffer lowering seek times that would normally be spent looking for the spread out directory structure.
• Non-volatile: because the buffer is non- volatile as opposed to volatile memory (volatile means it’s wiped when powered down) which is use din RAM, the buffer doesn’t lose any data in the event of a sudden power failure or reboot. You can even store the boot up data in the buffer.
• Actual hard drive usage: it is estimated that the platter will only be spinning between 1.25% and 10% of the time, compared to a normal hard drive.

Disadvantages

• Longer seek time for non-cached data: if you have to access data that isn’t in the buffer and the platter is at rest it takes some time to spin up the platter before searching for the data.
• Costs more
• More spin up: most wear and power usage happens during the spin up and spin down processes. Once spinning hardly any wear and tear is suffered by the hard drive. A hybrid drive spins up and down far more often that a standard hard drive.

The hybrid drive is a good idea but it seems to only serve as a bridge between HDD and SSD. And sadly it’s not a needed bridge. As far as my aim to conserve power goes, the SDD is superior to both the HDD and hybrid. Plus the SSD is faster, cooler running, faster and more reliable than both of its rivals.

The inclusion of a SSD instead of a HDD increases the price of a computer by a few hundred pounds depending on which one you’ve got. But all new technologies are expensive and the difference in price is falling all the time.

The military applications for SDDs are quite obvious. They run faster are more reliable, can endure extreme shock, high altitude, vibration and temperatures(from -40 degrees C to +85 degrees C), generate less heat and noise, longer life and they’re smaller and weigh less. This has been noted by manufacturers who want to make the most of this demanding market.

If the entire world adopted SSD (which will happen in the near feature) a lot of energy could be save. The individual save in power isn’t much but put it all together and it could make a big difference. And as Rudy Bruce, Exec. VP for Marketing and Sales and CMO at BiTMICRO Networks said “For storage users in the military and industrial markets, high disk capacities equate to longer hours, even days, of non-stop operation. Just like enterprise users, these markets desire continually increasing drive capacities to meet exponential growth in their storage requirements,”

Bibliography

BiTMICRO to Debut 416GB IDE Solid State Drive Packed in 2.5-inch Rugged Hard Disk Drive Footprint (2007) Retrieved January 7th 2008 from BiTMICRO Networks
http://www.bitmicro.com/press_news_releases_20070911.php

Hard disk drive. Retrieved October 22nd from Wikipedia
http://en.wikipedia.org/wiki/Hard_disk_drive

Hybrid drive. Retrieved October 22nd 2007 from Wikipedia.
http://en.wikipedia.org/wiki/Hybrid_drive

Perenson M. J. (2007). Solid-State Drives Versus Hard-Disk Drives in Laptops. Retrieved October 22nd 2007, from PC world website. http://www.pcworld.com/article/id,134185-page,2-c,thinandlightnotebooks/article.html

Solid state drive. Retrieved October 22nd 2007 from Wikipedia
http://en.wikipedia.org/wiki/Solid-state_drive