The Nand Flash Cache SSD Cash Dance

Posted on September 09, 2013 By Greg Schulz

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AS mentioned above, though, that benefit only exists if you can actually use or have the need for speed. If your applications cannot benefit from being able to dash using flash leveraging the need for speed, then that may not be the optimal solution. However, there are other considerations, including ability to do the same amount of work with fewer devices, removing complexity. Keep in mind that whenever you remove complexity costs are also removed.

Nand flash SSD also come in different variations (besides packaging) including single level cell (SLC), Multi-Level Cell (MLC), enhanced MLC (eMLC) and triple level cell (TLC), among others.

The difference in these in general is that as you add more cells stacked on top of each other your capacity goes up and costs come down. All good things right?

That depends, as there’s a catch. That catch is the more cells stacked on top of each other (e.g. MLC vs. SLC) results in lower write performance (still faster than HDD) along with more wear or reduced durability. This is because while nand flash has no physical mechanical moving parts, since it’s an electronic memory there are in fact cell gates that open and close to store data bits.

Now these gates are not like the mechanical hinged type ones you might be familiar with around your house. Yet these cell gates implemented in silicon (e.g. in the chips) do in fact wear out over time from repeated program/erase (P/E) cycles when data is stored. Note that P/E cycles only occur when data is written or saved, which also includes when data is deleted and garbage collection is performed.

Thus SLC nand flash has a higher cost, however a longer duty cycle so it’s better for write intensive data or as a write cache. MLC has a lower cost with more capacity, yet also lower durability, which is better for read cache or storing data that is seldom updated.

Some vendors and their pundits will dance or cheerlead the hype. There are others who practice the fear dance and that your data will disappear in a flash. So it’s best to find balance and relativity between the hype and fud. Keep things in proper context.

In case you are wondering, what do I use or have? I have nand flash SSDs in my laptop, as well as in my VMware servers that are companions complementing HDD, as well as Hybrid HDD (HHDD) also known as Solid State Hybrid Disks (SSHD). <P>

So to wrap up, nand flash SSD is in your future as it can help your data and applications dash (work faster) including as a cache to traditional HDDs. However, there is a catch, which is the cash, cost. On the other hand, look beyond the cash cost and consider how the nand flash SSD can help you dash, perhaps generating more cash by boosting productivity.

Greg Schulz is Founder and Sr. Analyst of independent IT advisory and consultancy firm Server and StorageIO (StorageIO).



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