Articles: Storage

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High-tech products usually pass a few typical stages of development on their way to conquering the market. First, there appear pilot and small-series samples in which the manufacturing technology is being polished off, the characteristic traits are being defined and various ideas, both lucky and not, are being tested. Next goes the period of maturing when product models change one another very quickly, their functionality constantly improving and their childhood diseases getting cured. And then goes the mature period proper. It is when the technology is developing at a slower rate, resulting in a steady improvement of key characteristics. It is during this period that the manufacturers come up with alternative technologies that might lead to new type products. The maturity will eventually transform into a decline, and it is very important not to miss this moment. All such processes go on very quick in the PC hardware industry and everyone can easily name a few examples of such cyclic development. This was the case with floppy diskettes and data CDs. The same goes for CPUs with their ever-changing architectures.

And for the last couple of years we have been witnessing one more example of this cycle as a new product type – a Solid State Drive (SSD) – is coming to market. The newcomer is so aggressive that hard disk drives, although obviously at their prime now, are already not superior to it in some aspects. Early SSDs could only rival HDDs in a few parameters, but the latest SSD models with multi-channel controllers deliver such a high performance that not only the fastest of HDDs but even RAID arrays made out of them fail to equal!

To be specific, early SSDs had the following indisputable advantages over HDDs:

  • Much lower data access time
  • Speed of reading randomly located data not much slower than that of reading sequentially located data
  • No moving parts hence zero noise
  • High tolerance to vibrations
  • Low power consumption

There were obvious downsides, though:

  • High data storage cost
  • Low speed of sequential operations in comparison with HDDs
  • Limited number of data write cycles in memory cells

The first problem could only be solved by a reduction of the price of flash memory. Watching the chip prices constantly declining in the last year, many analysts were very optimistic about the possibility of SSDs to quickly win a large market share. However, in the first half of 2009 the price of flash memory chips was growing up and it is only in the summer that there was a certain decline. A tough price competition was the main reason for that. Coupled with the reduced demand, it made the supply exceed the sales while the profitability was at its minimum. The market just could not digest that much of memory. To get any profit, the manufacturers increased their factory prices. As a result, SSDs have not been declining in price as quickly as predicted in the last year. Generally speaking, we don’t think that SSDs will become competitive to HDDs in terms of pricing any time soon. Today, the cost of 1 gigabyte of SSD storage varies from 2 to 5 US dollars whereas HDDs are as cheap as 0.1 US dollar and getting even cheaper. With such a huge gap in terms of pricing, most users are going to prefer the cheaper alternative and will only choose SSDs when they really need high performance.

The introduction of multi-channel controllers has helped SSDs not only overtake but even outperform HDDs in terms of sequential speeds. Even with relatively cheap MLC memory it is possible to create an SSD that has two times the sequential read speed of the best of modern HDDs. SSDs are not so brilliant at writing but at least comparable to HDDs in this aspect, too. And if you really want a high speed of writing, you may consider multi-channel SSDs based on SLC memory which is more expensive than the MLC variety and comes in smaller-capacity chips but ensures a better write speed and higher reliability.

The limited number of write cycles of flash memory cells is aggravated by the nonuniformity of typical loads (some cells work harder than others) and the lack of SSD-oriented optimizations in modern OSes. Many enthusiasts that used early SSDs as system disks were annoyed at their short service life due to the decay of memory cells. The first SSD that tried to solve that problem by utilizing effective controller algorithms was Intel’s X25-M. It was quite a surprise for us when we tested it (you can refer to this review for details about the deterioration of flash memory with use).

It is during that test session that we also encountered a specific feature of the current generation SSDs. Their performance depends on what the previous load has been and may degenerate greatly in some situations. We will talk about this problem later. Right now let’s take a look at the devices we are going to test. These are Corsair’s P128 and three SSDs from Intel.

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