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SSD vs HDD in 2012 Print
October 2012

SSD (Solid State Drive) as a technology for mass storage use has been under development for 40 years.   It has been discussed widely in the industry for mainstream use within the last 4 years and taken up by Compucon New Zealand for less than 14 months.  This timeline indicates SSD has made a lot of progresses and this article attempts to explain its status as in year 2012 and beyond.

HDD (Hard Disk Drive) has stayed on Winchester technology invented by IBM for about 40 years as well. Its main developments are in storage size and production cost but not in performance.  We are seeing 4TB from a SATA HDD for a retail price of a few hundred NZD only. 

These 2 strengths of HDD (large storage size and low price) happen to be the 2 weaknesses of SSD and the major weakness of HDD (low performance) happens to be the strength of SSD.  SSD has 2 more weaknesses (in reliability and lifespan) than HDD. 

In brief, HDD is based on rotating disk with magnetism for storage and SSD is based on a type of memory called NAND flash that is stationary and uses voltage for storage.   There are 2 ways of storage in NAND flash cells- SLC for single level cell and MLC for multi level cell. SLC refers to one bit per cell and MLC refers to 2 bits per cell.  SLC is more expensive, more reliable, and has a longer lifespan than MLC.  Since MLC SSD is already much more (over 10 times) expensive than HDD, SLC SSD is only used in top end applications and is not for the mainstream. 

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A new technology company turned up on the horizon and invented a few technologies on SSD called RAISE (see slide 1), Compression, and Zero Over-Provisioning which were detected on Compucon radars within the last 14 months.  These proprietary technologies have made SSD less expensive, more reliable, lasts longer (see slide 3), and further faster.  The advent of SAS600 or SATA 6Gb/s interface has helped release the full performance potential of SSD (see slide 2).  We are seeing SSD with a continuous Read speed of 550MB/s and continuous Write speed of 530MB/s.  Both speeds are above the last generation interface technology of SATA 3Gbps.  HDD is staying below 3Gbps at present unless RAID is applied. 

Whilst HDD vendors have consolidated into 2 major brands virtually forming a duopoly, many SSD vendors have appeared on the horizon and trying to turn the wave of fortune towards them.  Seagate is a major HDD vendor and they have attempted to join SSD by producing HDD models incorporating several GB of NAND cache additional to the original MB of memory cache inside the HDD enclosure.   According to performance benchmark test results, these hybrid HDD models are no where near SSD. 

It appears that we have to deploy SSD in reasonable storage size such as 128GB and more since size likes 8GB has not shown to be meaningful.   As of 2012, Compucon is promoting SSD for 3 uses.  The first is as the Boot Drive containing all applications leaving HDD for data storage.  The second is as the Cache for HDD RAID sets (this is the topic of a separate article).  The third is tiered storage for large businesses (again a separate article). 

Beyond 2012 are PCI SSD Drive and Enterprise MLC.  Wait for these new articles.