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True Customer Stories: We Want the Least Expensive SD Card Available

True Customer Stories: Solutions from the Desks of Delkin Customer Engineering

“We want the least expensive SD card available, our application is not write intensive.”

Background: As often happens in the flash business, Delkin was asked to bid on a quantity of SD cards for a new customer.  Despite early discovery efforts, the customer either did not know, or could not share, the usage model or specifics of the application, size and frequency of files written, or any data about the required operating temperature range.  The customer’s request was for “the least expensive SD card available”.  After qualification testing and approval, orders would be placed.  While the customer initially requested a TLC based solution, as other bidders were also sampling TLC flash solutions, Delkin recommended a Commercial Utility SD solution. The Commercial Utility SD solution features managed configuration and lifecycles like a true Industrial SD card, but utilizes less expensive MLC flash to offer cost savings over an SLC based equivelant.

Customer Story:  Almost six months after submitting samples the qualifications were nearing an end, and every SD card that had been submitted from each company had failed at various points during the testing.  The customer was getting anxious, as they had begun qualification testing with plenty of time to spare, and were nearing the product launch date without a single SD card approved for use in their host.

Because multiple brands and samples of cards had failed, the customer concluded that the problem did not lie perhaps in the cards alone, and the focus shifted to analysis of the host’s usage model during qualification testing. During that process, the customer tried to replicate a real-world usage model by cycling temperature up to 85C and writing a sample of the type of data that the host was designed to record, continuously.

Delkin Discovery:  Delkin’s Customer Engineering team went to work immediately, first analyzing the SMART data on the failed SD cards that had been returned after qualification testing.  This quickly revealed that the program/erase cycle counts performed during testing had exceeding the flash rating. All of the spare blocks had been consumed, leaving the card in a read-only state.  After further exploration, Delkin’s Customer Engineering team discovered that the application workload model consisted of very small writes, less than a page, to multiple partitions; this is considered random small writes, which increases write amplification.  Because of the customer’s write-intensive qualification process, they had written more than 9TB of data to the MLC flash, wearing out the card in a relatively short amount of time. The type of cards sampled were also susceptible to high temperatures, which made the failure occur faster.  While the Commercial UtilitySD card outlasted the competitors’ TLC cards, it still did not meet the target field life.

This situation is common when host manufactures are not fully aware of the host’s usage of the card.  The size of files being written, frequency of writing, and the operating temperature are just three aspects of choosing the right card solution for the host.  Delkin takes advantage of advanced testing equipment software programs to help determine, replicate, and analyze the real-world usage of each customer’s host application, and point towards the most ideal solution.

Delkin Solution:  Based on the analysis of the returned qualification cards, Delkin’s Customer Engineering team proposed testing a lower capacity SLC card, which would have the advantage of a much higher program/erase cycle rating, and due to smaller page and block sizes, lower write amplification than a MLC or TLC solution.  The customer re-ran qualification testing with the new Industrial SLC SD card samples that Delkin provided, and was able to pass the samples and meet the target launch date.

While the SLC SD card solution was more expensive than the TLC SD solution that the customer had originally requested, it performed flawlessly under the actual usage scenario, and enabled the customer to hit their new product launch date and begin collecting immediate revenue. By switching to a lower capacity SLC based card, the TBW was drastically improved, without the high price of adding additional un-needed storage capacity.  Delkin’s Customer Engineering team was also able to share all of the information that was learned about the host with the customer, and the customer was educated on aspects of “preventative maintenance” using the card’s SMART data.  This data then helped them to make updates to future versions of the host’s software to improve efficiency in regards to how the host wrote data to the flash, and also build in some SMART functionality.

 Lesson Learned:  It’s important to remember that a NAND flash memory card is much more complicated than just a “memory chip”. In this scenario where small writes resulted in high write amplification to the flash, spare blocks were retired earlier than necessary, and the high temp testing accelerated these failures.  By simply switching from a MLC or TLC card to an SLC card, program/erase cycles were increased by at least 20 times.  This exercise also helped the customer discover ways that the host program could be modified to become more efficient with the flash.

Lean on Delkin’s Technical Team:  Have you had a problem with your host storage?  The Delkin Customer Applications Team stands at the ready to be your trusted advisor for your host critical storage.  We have solved hundreds of complicated host failures and look forward to understanding your usage model for flash based Rugged Controlled Storage.

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