Advantages of Solid State Drives (SSD) in PXI Systems

Publish Date: Apr 01, 2013 | 10 Ratings | 2.90 out of 5 |  PDF

Table of Contents

  1. Overview
  2. Types of Solid State Drives
  3. Solid State Memory Options
  4. Advantages of SSDs
  5. SSD in PXI Systems
  6. Compatibility - PXI Controller
  7. Conclusion
  8. References

1. Overview

A solid state drive (SSD) is a storage device that stores non volatile data using solid-state memory. Solid-state memory is composed of electronic components that are based entirely on semiconductors. Since these drives do not have any moving parts they offer significantly reduced risk of mechanical failures resulting in improved system reliability.  They can also withstand extreme shock, high altitude and vibration, and other harsh operation environments.


Figure 1. 32 GB SATA-II 2.5" SSD 

Besides better tolerance for harsh operating environment and increased reliability, SSDs provide lower read and write seek times as compared to standard rotating medium hard-drives. This translates to higher sequential and random data read and write rates. Applications utilizing SSD drives will experience faster application load times and overall test-time savings due to lower file I/O processing times. A SSD fully emulates a traditional mechanical hard disk drive (HDD). This makes replacing the traditional HDD for an SSD in your current PXI embedded controller a quick and simple process.

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2. Types of Solid State Drives

There are two different types of solid state device designs that are commonly available. These are the Single Level Cell (SLC ) and the Multi Level Cell (MLC) designs. A cell can be considered as a low-level electronic storage component. A SLC based SSD stores one bit of data in each cell, leading to faster transfer speeds, lower power consumption and higher cell endurance. 

A MLC based SSD stores three or more bits in each cell. By storing more bits per cell, this type of SSD will exhibit slower transfer speeds, higher power consumption and lower cell endurance than a SLC device. MLC based designs need to incorporate complex data manipulation algorithms to store and retrieve correct data bits from the cells. The primary advantage of a MLC-based SSDs over SLC-based SSDs is the lower manufacturing cost per megabyte (MB).

Besides faster file I/O performance, SLC-based SSDs also offer longer life as compared to MLC-based SSDs. This is because the failure of a single storage cell in a SLC-based SSD will results only in the loss of a single data bit. On the other hand, failure of a single storage cell in a MLC-based SSD will results in loss of multiple data bits.  

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3. Solid State Memory Options

Solid state drives can use different types of memory elements such as Static Random Access Memory (SRAM), Dynamic Random Access Memory (DRAM), or NAND Flash memory to store the data bits. SRAM is a semiconductor memory type that does not need to be periodically refreshed. Although it exhibits data reminisce, SRAM is still volatile that means the data will eventually lost if the memory is not powered. DRAM requires that the stored information to be periodically refreshed. This requirement makes DRAM dynamic compared to SRAM which is static. DRAM is similar to SRAM as it is a volatile memory and it loses its stored information when the memory is powered down. A SSD that uses SRAM or DRAM, instead of flash memory is often called a RAM-drive.

The last option for memory is NAND Flash. NAND Flash memory is a specific type of EEPROM that can be erased and programmed in large blocks. NAND Flash memory is non-volatile, which means that no power is needed in order to maintain the information that is stored in the chip. In addition, flash memory offers fast read access times (although not as fast as the volatile DRAM memory typically used for main memory in PCs) and better kinetic shock resistance than traditional mechanical HDDs.

From the options available, solid state devices are commonly composed of either non-volatile NAND Flash memory or volatile DRAM memory. Most SSD manufacturers use non-volatile NAND Flash memory to create more rugged and compact alternatives for the consumer market. Flash SSDs are significantly slower than DRAM SSDs that have fast data access but they do not require batteries to maintain the stored information, thus allowing manufacturers to replicate traditional mechanical HDD form factors (1.8-inch, 2.5-inch, and 3.5-inch). In addition, the non-volatility allows flash SSDs to retain data even during sudden power outages. DRAM based SSDs typically incorporate internal battery and backup disk systems to ensure data persistence. Upon the restoration of power, the stored data is copied back from the backup disk to RAM, and the SSD resumes normal operation.

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4. Advantages of SSDs

Solid state drives (SSDs) have many advantages over traditional mechanical HDDs. Many of the advantages are a result of SSDs not having any moving parts. While a traditional drive has drive motors to spin up the magnetic platters and the drive heads, all the storage on a solid state drive is handled by flash memory chips. This feature provides lower power requirements, faster data access, and high reliability.

Reliability

Due to the lack of moving parts, SSDs are less likely to fail in extreme temperatures and high shock and vibration environments. The ability to operate in extreme temperatures ranging from 0°C to +70°C, expands the number of applications that can be addressed by a SSD based system. 

Reliability is also an important factor for portable systems. Traditional HDD can be critically affected if exposed to jarring movements from an impact. Since the SSD stores all its data in memory chips, there are no moving parts to be damaged in the event of an impact. This lack of moving parts almost completely eliminates the risk of mechanical failure. Table 1. Compares the key reliability features of the SSD, standard HDD and an extended temperature HDD. These features can be used for determining which specific hard drive will be suitable for a specific application environment.

  Samsung 32GB SATA SLC SSD Intel 32GB SATA SLC SSD Intel 250GB SATA MLC SSD Fujitsu 160GB SATA 5400RPM HDD Seagate 80GB PATA Extended Temp HDD
MTBF 2,000,000 Hours 2,000,000 Hours 1,200,000 Hours 300,000 Hours 750,000 Hours
Operating Temperatures 0°C - 70°C 0°C - 70°C 0°C - 70°C 5°C - 55°C -30°C to 85°C
Humidity up to 90% 5% - 95% 5% to 95% 8% to 90% 5% to 90%
Shock (Operating) 1500G at 0.5ms half sine wave 1000G at 0.5ms half sine wave 1500G at 0.5ms half sine wave 300 G at 2ms half sine wave 300 G at 2ms half sine wave
Shock (Non Operating) 1500G at 0.5ms half sine wave 1000G at 0.5ms half sine wave 1500G at 0.5ms half sine wave 400G at 0.5ms half sine wave 400G at 0.5ms half sine wave
Vibration (Operating) 20G Peak (10 - 2000Hz) 2.17G Peak (7 - 800Hz) 2.17GRMS (7 - 800Hz) 1.0 G Peak (5 - 500 Hz) 2.0 G Peak (5 - 500 Hz)

Table 1. Key reliability features of the SDD, standard HDD, and an extended temperature HDD

Data Read & Write Rates

Data access rates are extremely important to a test, measurement, and industrial applications. Data in an SSD can be read nearly instantaneously since the drive does not need to spin-up the drive platter or move the drive heads as in the case of traditional HDD. SSD exhibit significant increase in the read/write rates due to the lack of these mechanical delays. This performance boost increases user productivity by enabling faster loading of applications, increased data read and write rates and decreased system boot-up/shutdown time. Refer to table 2. for comparison of data transfer rates for the SSDs and regular HDDs.

  Samsung 32GB SATA SLC SSD  Intel 32GB SATA SLC SSD Intel 250GB SATA MLC SSD Fujitsu 160GB SATA 5400RPM HDD Seagate 80GB PATA Extended Temp HDD
Average Sequential Read Rate 79.9 MB/s 176.7 MB/s 171.0 MB/s 56.2 MB/s 33.5 MB/s
Average Sequential Write Rate 72.5 MB/s 155.6 MB/s 153.1 MB/s 56.2 MB/s 33.4 MB/s
Average Access Time 4.4 ms 0.15 ms 0.21 ms 12.6 ms 12.2 ms

Table 2. Comparison of data read and writes rates between SSD and regular HDD on a PXI-8108 Embedded controller

Performance

Besides faster read and write rates SSDs also have better deterministic performance as compared to regular HDDs. Unlike traditional HDDs, the performance of a SLC SSD is nearly constant and deterministic across the entire storage space. This is due to the constant seek times offered by a SSD. There are two key reasons for this performance advantage. The first is file fragmentation. Files become more fragmented over time, requiring a traditional HDD to perform additional seeks to retrieve a complete file. This reduces the effective performance of the HDD as compared to the SSD, which has much lower seek times. The second reason is the manner in which data is stored on an HDD. When data is first written to a HDD, it is stored in the sectors near the outer edge of the spinning platters, which move faster as compared to the sectors closer to the center of the platter. As the HDD fills up, data is written to the slower-moving inner sectors, reducing write and read speeds up to 50%. Since SSDs do not have any moving parts they are able to maintain the read and write performance through the entire capacity of the drive. Figure 2 compares the performance of the Seagate 2.5in SATA Extended Temp HDD and the Samsung 2.5in SATA SLC SSD reading data across the entire disk. As the graphs illustrate, as you move from the outermost rim to the inner rim of the traditional HDD there is a significant drop in read rates, whereas the rates remain fairly constant for the SSD.


Figure 2. Left - SLC SSD Reads across the entire drive (Left – Outermost sector, Right – Innermost sector). Right - HDD Reads across the entire drive (Left – Outer rim, Right – Inner rim)

Power Consumption

For portable systems, power consumption is an important factor. SSD uses far less energy than regular traditional HDDs as there is no power used to drive motors in a SSD. The traditional hard disk industry has taken steps to address power requirements of traditional drives by implementing idle drive spin down and the development of hybrid HDDs, but even with both of these implementations, regular HDDs consume more power than a SSD. Table 3 compares the power consumption for the SSD, standard HDD and an extended temperature HDD. 

  Samsung 32GB SATA SLC SSD  Intel 32GB SATA SLC SSD Intel 250GB SATA MLC SSD Fujitsu 160GB SATA 5400RPM HDD Seagate 80GB PATA Extended Temp HDD
Read/Write 0.41 W 2.4 W 0.50 W 1.9 W 1.9 W
Idle 0.32 W 0.06 W 0.10 W 0.60 W 0.99 W
Standby 0.24 W 0.06 W 0.10 W 0.13 W 0.26 W
Sleep 0.24 W 0.06 W 0.10 W 0.13 W 0.26 W

Table 3. Power consumption between SSD, standard HDD and extended temp HDD

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5. SSD in PXI Systems

Every test, measurement and industrial control application is unique and has very specific needs. PXI is already being used in many of these application and the use of SSDs in PXI systems will help expand the usability of PXI in to applications that have high operating temperature, shock and vibration requirements. Not only does a SSD improve the availability of a PXI system, it also the performance capabilities of such a system .

Faster Test Times

Many test and measurement applications require intensive reading and writing of data to disk for either data logging or for offline analysis. The use of SSDs in a PXI based system for such applications will allow reduction in test time because of performance advantages of SSDs over regular HDDs. 

Improved Reliability and Durability

PXI specification defines requirements that make the PXI systems well-suited for harsh environments. PXI systems have many components that need to be able to withstand these environments, which include the controller, chassis, and modules. A PXI embedded controller is an important factor when considering the availability and ruggedness of a PXI system. As indicated in Table 1, SSDs have a much higher mean-time before failure (MTBF) and better tolerance to high shock and vibration as compared to traditional HDDs. The use of SSDs in a PXI embedded controller will result in the overall system having higher availability and a longer life span. However, it is critical to understand that one must also consider the availability and ruggedness of the PXI chassis and the modules to determine the overall specifications of the  PXI system. The availability and ruggedness of PXI embedded controller increases with the use of SSDs but the overall availability and ruggedness of the system would be defined by the specification of the PXI chassis. 

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6. Compatibility - PXI Controller

When choosing a PXI controller for a system, ensure that it is going to be compatible with the SSD option. The incompatibility is due to the specific controller having a PATA interface to connect to the drive. The 32 GB SSD option and 250 GB HDD option have the SATA interface. 

PXI Controller Compatibility List


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7. Conclusion

A solid-state drive is usually based on flash memory chips and does not contain any moving parts because of which it is able to tolerate exposure to higher levels of shock and vibration than traditional mechanical HDDs.  SSDs also offer significantly better read and write rates over standard HDDs, allowing faster application load times and lower test-times. The use of SSDs in PXI embedded controller allows PXI based system to be used demanding applications such as industrial control and portable measurement systems.

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8. References

Developer Zone Tutorial: Selecting Hard Drives for Test, Measurement, and Control Systems

Developer Zone Tutorial: Best Practices for Building and Maintaining PXI Systems

KnowledgeBase 2UDE586W: Are Solid-State Flash Drives Compatible with PXI Embedded Controllers?

NI PXI Embedded Controllers

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