Solid State Drive (SSD)
Data Storage: Solid State Drive vs. Hard Disk Drive
Faster, solid state data storage used in place of conventional electromechanical hard disk drives (HDDs) in computers and servers.
Item ID: 159
Technical Advisory Group: 2013 Information Technology TAG (#8)
Average TAG Rating: 3.23 out of 5
TAG Ranking Date: 10/25/2013
TAG Rating Commentary:
- Valid for performance - small energy savings. Waste of incentive money. Facebook "cold storage" is much better concept - just turn OFF hard drives when not needed.
- Difficult to implement and verify.
- I believe this has to be a leading emerging tech.
- Not an ET.
- Cost per gig still high but coming down.
- Long term storage may require a duplicate storage strategy.
- Very hard to control what tenants buy, long payback.
- SSDs not only provide much faster data read and write operations, but also have a much smaller energy footprint due to their low voltage operation.
Existing hard disk drives (HDDs) use magnetically encoded disks to store and access data. While HDDs have a proven track record, newer forms of memory are making them obsolete.
"SSDs had origins in the 1950s with two similar technologies: magnetic core memory and card capacitor read-only storage. Electronic storage approaches have continued to evolve. SSDs with NAND technology, or flash memory, were first introduced by M-Micro in 1995. "They had the advantage of not requiring batteries to maintain the data in the memory (required by the prior volatile memory systems), but were not as fast as the DRAM-based solutions. Since then, SSDs have been used successfully as HDD replacements by the military and aerospace industries, as well as for other mission-critical applications" (Wikipedia, 2013).
Solid state drives (SSDs) and flash memory deliver better performance for read access and use less energy. When compared against one another, flash drives accessed data 10 to 100 times faster than HDDs, and SSDs accessed the data over 65 times faster than HDDs. They do not have this same advantage for write applications, however. In terms of energy efficiency, SSDs delivered up to 237 MB per joule, flash drives delivered up to 150 MB per joule, while HDDs topped out at 28 MB per joule. (Mordvinova, 2009)
This higher performance comes at a price: a 1 TB internal SSD from Samsung costs roughly $600, while a 1 TB internal HDD costs roughly $100. As the price of SSD and flash drives continues to drop, these newer forms of memory promise to reduce the energy consumption of computers while simultaneously improving performance.
Baseline Description: Reading and Writing data to an electromechanical 1 TB SATA disk
Baseline Energy Use: 175 kWh per year per unit
The baseline technology uses spinning disks, like CD's. Spinning the disk uses power. The power used by a spinning disk, 24/7/365 is about 175 kWh/yr. For purposes of apples-to-apples comparison, assume that this is a one terabyte drive. Assume that it is idle about half of the time and varies between streaming audio or video, database calculations, and maximum read-write loading when active. (Otto, 2013)
Manufacturer's Energy Savings Claims:
"Typical" Savings: 20%
Savings Range: From 1% to 60%
We have not been able to find specific levels of energy savings claims from manufacturers. However, they will readily say that they do save energy, and they give product specifications from which one can calculate savings with certain assumptions about use, such as how much each drive is in idle, sleep, or hibernate mode. Complicating the calculation, however, is determining an apples-to-apples comparison. As of the end of 2013, enterprise-quality SSDs are mostly available in 512 GB capacity and less, whereas HDDs are easily available up to 4 TB capacities. If an apples-to-apples comparison is a 512 GB SSD vs. the same capacity HDD, then it is easy to show 80% savings or more (Otto, 2013). However, if an apples-to apples comparison is what you may be likely to buy -- that is, for instance, a 2 TB HDD or four 512 GB drives, you may not save anything at all. We believe that most manufacturers would be comfortable in claiming that SSDs will save about 20% or more of the energy of HDDs.
Best Estimate of Energy Savings:
"Typical" Savings: 50%
Low and High Energy Savings: 10% to 93%
Energy Savings Reliability: 3 - Limited Assessment
This estimate is based on a standard hard drive using 175 kWh per year, and a solid state drive using 20 kWh. This is a fairly typical estimate for a 1 terabyte drive in Nov. 2013. That gives about 89% savings. With this technology improving so rapidly, and the standard hard disk not as fast, we are assuming slight continued improvement by the time this is published, so we rounded the savings up to 90%. That will depend, however, on several assumptions. One variable will be how much each drive is in idle, sleep, or hibernate mode. Complicating the calculation is determining an apples-to-apples comparison. As of the end of 2013, enterprise-quality SSDs are mostly available in 512 GB capacity and less, whereas HDDs are easily available up to 4 TB capacities. If an apples-to-apples comparison is a 512 GB SSD vs. the same capacity HDD, then it is easy to show 80% savings or more (Otto, 2013). However, if an apples-to apples comparison is what you may be likely to buy -- that is, for instance, a 2 TB HDD or four 512 GB drives, you may not save anything at all. The estimate of 50% savings is based on the idle-active ratio assumed by Otto, and assuming your choice is to buy a single 2 TB HDD in place of four 512 GB or two 1 TB SSDs. Typical examples of these might save 30% over HDDs. Furthermore, since using less energy in storage access would reduce the cooling load in the data center, and would save some cooling energy as well. We estimate the average data center Power Usage Effectiveness is 2.6, so it is fair to multiply the storage energy savings by 1.67 to get energy savings equivalent to 50% of the storage energy used by the equivalent HDD.
This estimate of savings does not take into account reduced cooling needs. SSDs can withstand much higher temperatures than HDDs and virtually require "no" cooling. If this could be implemented throughout a data center to significantly reduce cooling loads, the total savings from implementing this technology could be much greater, depending on other measures already taken to save energy.
Energy Use of Emerging Technology:
87.5 kWh per unit per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Currently no data available.
Installed first cost per: unit
Emerging Technology Unit Cost (Equipment Only): $600.00
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $50.00
Baseline Technology Unit Cost (Equipment Only): $100.00
This estimate was based on a spot comparison in November 2013 on Newegg.com, comparing the cost of a client-quality SSDs: SAMSUNG 840 EVO MZ-7TE1T0BW 2.5" 1TB SATA III TLC Internal Solid State Drive (SSD) or Crucial M500 960GB SATA 2.5" 7mm (with 9.5mm adapter) Internal Solid State Drive CT960M500SSD1 versus various 1TB client-quality HDDs available at under $100. The installation charge is based on an estimate from the WSU Energy Program IS staff estimate of 30 to 50 minutes to install, assuming it can be done with internal staff.
Simple payback, new construction (years): 63.5
Simple payback, retrofit (years): 82.5
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
From Wikipedia (Wikipedia, 2013): “A solid-state drive (SSD) (also known as a solid-state disk or electronic disk, though it contains no actual "disk" of any kind, nor motors to "drive" the disks) is a data storage device using integrated circuit assemblies as memory to store data persistently...SSDs had origins in the 1950s with two similar technologies: magnetic core memory and card capacitor read-only store (CCROS)."
Electronic storage approaches have continued to evolve. SSDs with NAND technology, or flash memory, were first introduced by M-Micro in 1995. "They had the advantage of not requiring batteries to maintain the data in the memory (required by the prior volatile memory systems), but were not as fast as the DRAM-based solutions. Since then, SSDs have been used successfully as HDD replacements by the military and aerospace industries, as well as for other mission-critical applications" (Wikipedia, 2013).
Still, until 2009, most SSDs used dynamic random access memory (DRAM). It is orders of magnitude faster than HDDs, but is more expensive, and it is "volatile" memory, meaning the data needs to be refreshed periodically (several times a second) or it is lost. Since 2009, most SSDs have used NAND or "flash" memory. This is a non-volatile memory, so it uses no power to retain the data when it is just being stored. This makes it significantly more energy-efficient than either DRAM or HDDs.
The primary advantage of SSDs over HDDs is a read speed orders of magnitude (approaching 100 times) faster than HDDs. Write speeds on a new SSD can also be very fast. However, once an SSD has fully been used, write performance degrades noticeably, proceeding more at the erase speed (since data is having to be erased to make room for more data), which is much slower, and may not be faster than an HDD. Thus, they are very well suited to low write/high read applications. ( Energy Star, 2013)
Solid state drives are well-established in the market and are easily available from several manufacturers, notably Seagate, Toshiba, Western Digital Technologies, and Samsung. A few examples are listed in the Product Information section.
The standard technology that solid state drives (SSDs) replace in computers, consumer electronic devices, and servers are electromechanical hard disk drives (HDDs) with Serial Advanced Technology Attachment (SATA) bus interface.
SSDs are easily available, and have been for several years. Prices have dropped dramatically in 2012 and 2013, and are expected to continue to do so. They are now affordable enough that many enterprises are beginning to deploy them for performance reasons more than for energy savings. "the percentage of IT administrators using SSDs on disk arrays and servers was up to 20% in 2012."
The main advantage of SSDs over HDDs is speed. The following table compares various speed-related characteristics of SDDs to HDDs.
| Characteristic ||Solid State Drive ||Hard Disk Drive |
| Start-up time || Almost instantaneous. May need a few milliseconds to come out of an automatic power-saving mode. || Several seconds |
| Random access time || Typically under 0.1 ms || 2.9 to 12 ms |
| Read latency (delay) time || Low || Much higher than SSDs. Latency will depend on the location of the data on the disk relative to the read-head. |
| Data transfer rate || Consumer products typically 100 to 600 MB/s. Enterprise-quality devices can have data transfer rates of 2 GB/s or higher. || Typically 140 MB/s |
| Fragmentation || Since location on the disk does not affect transfer rate, fragmentation of files is not a problem. || File fragmentation can affect access time because each fragment may require spinning of the disk to access. Defragmentation is required periodically for maintenance. |
Because of the almost instantaneous access time, these are ideal in applications where many users are trying to access the same drive at the same time.
SSDs also operate almost totally silently and can tolerate much higher temperatures and typically do not require special cooling. HDDs lose life expectancy over 95 F (35 C), and reliability is compromised above 131 F (55 C). SSDs also tend to be more reliable in general, though failures are sometimes more catastrophic that hard drives. They are also much more resistance to shock and vibration, making them a good choice for places where this is an issue, such as laptops.
End User Drawbacks:
Solid state drives, as of late 2013, are still significantly more expensive than standard hard disks, and wear out more quickly.
According to Adrian Otto, on his blog:
Reasons why NOT to switch to SSD drives
- If you need a lot of storage. The cost per GB of the SSD storage is considerably higher than the cost per GB of SATA storage, even considering the performance and power savings.
- If you are constantly writing to the hard drives over and over. SSD drives to have a limited duty cycle, and in general may be less durable than regular hard drives. Eventually they do wear out, just for different reasons than drives with moving parts. However, most of the drives that are on the market today are rated for MTBF durability that’s comparable to what traditional hard drives offer.
- You run your data center on solar power (yeah, sure you do). Seriously, if your cost for power is dirt cheap, and you need a lot of storage, then regular hard drives may be a better value for you. (Otto, 2013)
The other thing to be aware of is that with lots of re-writing, performance will degrade. At advertised and new speeds, SSDs are dramatically faster than HDDs, but performance degrades noticeably with use. Partly that is because erase speed is much slower than write speed, and once a disk is full, any writing will be over-writing old data, slowing performance from new down by a factor of five or more. In addition, software may not be written to fully take advantage of SSD performance, so the improvements over HDDs may not be as much as advertised (Polte, 2009). Some researchers question whether an SSD, once full, under current practices, really performs that much better than HDDs. (Boboila, 2011)
Operations and Maintenance Costs:
Baseline Cost: $0.00
per: unit per year
Emerging Technology Cost: $0.00
per: unit per year
Other than replacement costs, there is really no maintenance to SSDs or HDDs. HDDs do need to be defragmented once in a while, but that can be set up to happen automatically during slow computational times through software, so the labor and out-of-pocket costs will be minimal. On average, SSDs do not last as long as HDDs, so replacement costs will be higher, but either one should last as long as most IT hardware is kept these days (4-5 years).
Anticipated Lifespan of Emerging Technology: 5 years
A few years ago, some of the concerns about SSDs is that they were less reliable than HDDs and there was a possibility of catastrophic failure, losing all the data from an entire SSD. Those concerns are still relevant, but much less so than a few years ago. An SSD does have a limited number of read-write cycles before they fail, but this has been improving, and most drives now come with management software that controls which sectors are used for wear-leveling, so that most sectors will get even wear, which helps extend the life of the drive. Enterprise-quality drives can now considered to be essentially error-free and have a 15-20 year or more technical life. In practice, most of this kind of equipment is upgraded in five years or less, since the quality, performance, and storage density will likely be much greater in 5 years, justifying an upgrade long before failure.
The main competing technology is solid state hybrid drives (SSHDs). They have a mechanical hard drive at the core and NAND (flash) memory to supplement. They come with controllers to use the flash memory for the frequently-used data for fast access, and use the hard drive for less frequently accessed data, taking advantage of the best properties of both technologies. They provide much faster access to frequently-used data than a hard drive, and much more economical storage for longer-term storage, providing the best of both worlds.
Reference and Citations:
Does SSD Power Savings Pay for Itself?
Adrian Otto's Blog
The short answer is "no." A solid state drive (he didn't specify the size -- 1 Terabyte?), using Adrian Otto's assumptions, saves, on average, about 80% of the energy of a standard hard drive, saving about 20 W over a hard drive, or 175 kWh per year per drive for a server running 24/7, or nearly $16/yr. With an expected lifetime of five years, they would save about $80 each. Add HVAC savings, and you could get $100 savings per drive. As of mid-2013, they cost $2-300 more than a standard hard drive.
Understanding Performance in Solid State Disks
Los Alamos National Laboratory
Study of Solid State Drives performance in PROOF distributed analysis system
Brookhaven National Laboratory
A Semi-Preemptive Garbage Collector for Solid State Drives
Oak Ridge National Laboratory
Coordinated Garbage Collection for RAID Array of Solid State Disks
Oak Ridge National Laboratory
Better Management of Data Storage
A Storage Technology Cage Match
Library of Congress
Solid State Drives
Joint Electron Devices Engineering Council
In September 2010 JEDEC announced the publication of two widely anticipated standards for solid state drives: JESD218 Solid-State Drive (SSD) Requirements and Endurance Test Method and JESD219 Solid-State Drive Endurance Workloads.
Performance Models of Flash-based Solid-State Drives for Real Workloads
Hystor: Making the Best Use of Solid State Drives in High Performance Storage Systems
Intel Labs/Ohio State University
Analytic Modeling of SSD Write Performance
USB Flash Drives as an Energy Efficient Storage Alternative
University of Heidelberg
Power Point presentation of the paper submitted for the 2009 10th IEEE/ACM International Conference on Grid Computing, Banff, Alberta, Canada
USB Flash Drives as an Energy Efficient Storage
University of Heidelberg
Paper presented at the 2009 10th IEEE/ACM International Conference on Grid Computing, Banff, Alberta, Canada.
Shows that flash drives can be a viable alternative to hard drives when used appropriately, and can save energy.