More memory means a longer SSD lifespan

Tests show disk I/O can be drastically reduced with increased memory, extending the life of a SSD.

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Twenty years ago, a Unix hacker friend would intone "Memory equals performance" like a mantra. Over time I've come to agree with that assertion anecdotally, but now a series of test show that memory not only translates into performance, but a potentially longer lifespan for your SSD as well.

SSD drives are still relatively new to the market and their makers are still gathering metrics on wear and mean time before failure. Unlike a hard drive, which uses a magnetic metal platter, SSDs are memory chips and there are three types of chips: single level cell (SLC) and multi-level cell (MLC). In MLC, you can have either two or three levels.

SLC uses a single memory cell to hold one bit of data. MLC uses two or three cells to hold two or three bits of data. What that means is in an MLC drive, a cell may be accessed two or three times as often as an SLC drive, and flash memory eventually wears out from read and write access.

SLC is used in enterprise-class SSD drives while MLC is used in consumer SSDs. There's a reason for that; MLC is cheaperm about one third of the price of SLC. On the flip side, a MLC cell is typically rated at 10,000 erase/write cycles before it dies and is unusable. As more and more cells die, the capacity of the SSD will shrink and data will be lost. A SLC cell can last up to 10 times longer than an MLC before failing.

So SLC is the memory of choice for its reliability and durability. But that doesn't mean a SSD in your PC will up and die in a year just because it uses MLC. Manufacturers of SSD drives with MLC cells have their tricks for reducing the impact, like wear leveling across memory and putting in extra memory, so as cells wear out, new ones replace it.

And the folks at Tom's Hardware Guide have found you can greatly extend the life of your SSD with more DRAM as well. They conducted tests of disk usage on a 4GB machine vs. a 16GB machine and the results were indisputable.

"In essence, there is no such thing as too much memory in a desktop with solid-state storage. The more RAM you add, the better off endurance looks, and the more I/O performance you get from the storage subsystem," the tester wrote.

The test involved running three memory-intensive applications and measuring the amount of disk I/O done during the process. This was done on one system where the only difference was the memory. For one round of tests it had 4GB and for another round, 16GB of memory.

Now, you will always have a swap file on your computer regardless of memory, unless you go into advanced Windows 7 settings. Windows by default makes a swap file that is twice as large as your physical memory, so a 16GB machine has 32GB of swap file taking up space on the SSD. Yes, you can relocate the swap file off the SSD but that kind of kills the point of an SSD in the first place.

However, having more memory means fewer disk writes to the swap file, and the Tom's Hardware tests showed that. A 16GB machine compiled the Google Chrome source code in Visual Studio 2012 with 64% less disk I/O than on the 4GB machine. The other tests were substantive as well, but not as drastic in the reduction in I/O as the Chrome compile.

The SSD makers are promising up to 10 years even on an MLC drive, but we are still in somewhat uncharted waters with these things. The bottom line is you want to reduce disk writes as much as possible, and more memory is the way to do it.

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