Solid State Drives (SSD) are storage devices that have solid state memory, emulate a hard disk drive to store data, and uses hard disk drive (HDD) interfaces as well as Non-HDD interfaces. CPU performances have increased due to multi-core architecture, but HDD performance has stalled due to mechanical parts. Due to this, they have become bottlenecks while accessing data. An SSD with NAND flash memory can improve access speeds.
Advantages of SSDs
SSDs are very expensive. However, due to the benefits that are offered by the SSDs, more and more enterprises are considering the use of SSDs over HDDs. The SSDs offer higher sustained access speeds. They have no moving parts and hence operate noiselessly, generates les heat, and uses less power. Due to the lack of moving parts, it is free from failures due to shock, temperature fluctuations, and vibration, so reliability is high. Annual Fail Rates (AFR) for SSDs was found to be 90% or higher due to which down time and IT costs for troubleshooting are vastly reduced. For applications where there is a huge input/output operation per second (IOPS) requirement, SSDs are preferred, to break the logjams. So, a database server serving many queries would be a good candidate for an SSD, which is the case in an Online Transaction Processing (OLTP) System. Similarly, an application like Netflix, which supplies Videos on Demand (VOD) can benefit from SSDs due to the demand for rapid upload of large amounts of data.
In a virtual desktop infrastructure (VDI), there will be instances of boot storm (where many concurrent users try to login), and these are not handled well by traditional HDDs and cause logjams. Using SSDs in such situations can help relieve the system. The SSDs come in four form factors such as MLC, eMLC, SLC, and TLC. Of these SLC (Single level cell) is the costliest option but offers very high reliability and can be used based on the need for reliability. All others can either use eMLC (enterprise grade multi-level cell), which is cheaper. For consumer or non-critical usage, MLC SSDs are still cheaper, but better suited. Using SSDs, the performance of VMware hosts needing local data storage, can be improved by improving cache performance. So, application that needs faster data access or high IOPS or is critical, or needs high reliability is a candidate for using SSDs.
Limitations or disadvantages of SSD
The SSDs are expensive by many orders. Within SSDs, SLC are very expensive, followed by eMLC, and the least expensive is MLC, which is still costs many times than a HDD. Currently the price/GB of data stored is very high for SSDs, but for applications that require high reliability, SSDs might be an option. The performance of the SSDs is affected by how full the drive is. Users will have to move data to traditional hard disks or purge data regularly, if access speeds have to be maintained. Unlike HDDs which fail slowly and give ample warnings, SSDs fail suddenly, putting data at risk. SSDs, if used improperly, may not help in improving performance. Each bottleneck has to be examined to see if SSDs will really solve the problem. As mentioned earlier, if SSDs are used for a web server, there might be negligible performance improvements, however, if used for database servers, the performance improvement is considerable.
Recommendations
In both cases, Delaware Health and Social Services (DHSS) currently uses 15,000 rpm drives as tier 1, probably in RAID (redundant array of independent disks) formation, while Disabled American Veterans uses SSD in laptops. Figure 1 shows a comparison of total cost of ownership of replacing a RAID array of 48 HDDs (15,000 rpm) with seven SSDs. For an enterprise such as DHSS, long-term gains are possible with judicial use of SSDs as the total cost of ownership (TCO) is about 60% less than when using HDDs. SSDs offer a good benefit where the system performance is limited by I/O performance, the files that are used are small random files, and the requirement is for low power consumption. If the system is limited by CPU performance, then using SSDs will not help.
Figure 1: Total system cost (Intel Corp.)
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For the Disabled American Veterans, using SSDs instead of Laptops, the following savings in TCO can be achieved. IT labor costs are reduced due to reduction in costs for PC repair or replacement due to lower failure rates, and savings due to reduction in trouble shooting and downtime. HDD suffer significant drop in performance and reliability after 3 years requiring refreshes. PCs with SSDs require less annual support and increases the annual refresh cycle of the PCs. The higher performance due to SSDs will result in productivity gains. Figure 2 gives the annual savings due to the use of SSDs in PCs. Hence it is recommended that Disabled Americans Veterans adopt SSDs for its laptops.
Figure 2: Annual savings per PC with an SSD
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SSDs in Forensics
SSDs use flash memory. Wear levelling and over provisioning are techniques used to ensure that parts of the flash memory do not get excessively worn out. Due to these techniques, junk data gets deleted. This deletion can happen very quickly, sometimes in milliseconds. In a HDD, the data is recoverable as any data that is deleted is not really deleted, but its location is marked as available and overwritten with new data. However, an SSD with TRIM command enabled, moves the deleted areas out of logical file space into the overprovision space. The space is then eventually purged. Once purged, the data cannot be retrieved by a forensic investigator. If somebody who had committed a fraud deletes some incriminating files and TRIM is enabled on the SSD, then those files are purged immediately and are not available for the forensic investigator to recover later. Due to the nature of the flash memory, any command to format or erase the drive can clear the data from the drive in minutes or even seconds. Once cleared, it cannot be retrieved. Write-blockers can be used to stop the TRIM command, but they cannot stop wear levelling algorithms. Using dechipping, the flash memory from the SSD can be removed and imaged. This image might not be useful as the data allocation through LBA-PBA (Logical Block Address-Physical Block Address) mapping is randomised but that map is missing. Moreover, proprietary compression schemes are to store data resulting dechipped data being difficult to decipher. When using dechipped images as evidence in the court of law, the court is interested in the LBA structure of the files (or as the OS system sees the data) rather than as a PBA, which is how the SSD stores the data. So, the LBA has to be arrived at and the data remapped and presented as evidence in the court.
References
Jeff Janukowicz, R. P. (2015). The SSD-Enabled PC: Total Cost of Ownership Is Beyond Compelling. Framingham, MA: IDC.
Nelson, F. (2014, May 29). Advantages of Flash in the Data Center: Not Just a Flash in the Pan. Retrieved from tomsitpro.com: http://www.tomsitpro.com/articles/flash-data-center-advantages,2-744-2.html
Posey, B. (n.d.). Will SSD performance benefit your data center? Retrieved February 9, 2016, from searchdatacenter.techtarget.com.
Sliwa, C. (2012). Enterprise IT shops now choose SSD storage. Retrieved from searchsolidstatestorage.techtarget.com/: http://searchsolidstatestorage.techtarget.com/feature/Enterprise-IT-shops-now-choose-SSD-storage
Wiebe, J. (2013, May 28). Forensic Insight into Solid State Drives. Retrieved from forensicmag.com: http://www.forensicmag.com/articles/2013/05/forensic-insight-solid-state-drives
Wong, G. (2013). SSD Market Overview. In A. M. Rino Micheloni, & K. I. Schmitt-Landsiedel (Ed.), Inside Solid State Drives (SSDs) (Vol. ADVANCED MICROELECTRONICS 37, pp. 1-18). New York, NY: Springer.
