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SD card duration
#1
Before you read on watch this story first: https://insideevs.com/news/376037/tesla-...ory-issue/

So categorize your containerized applications how write intensive they are stressing the non-volatile storage media used on embedded devices such as netPI.

Critical are those applications writing data at high volumes like databases. But not only the applications could get critical:
Docker daemon logs all container's console activity too. So if you have an application running at debug level for example that outputs tons of textual information on the console (even no one would read it) will lead to a worn-out-effect easily too.

netPI includes an 8GB micro SD card of type MLC-NAND from seller company Xmore with part number SDU008GXASMM-001E (Nowadays it is SANDISK SDSDQAF3-008G-I). The most critical thing about a NAND flash memory is its finite number of erase/program cycles (P/E cycles) also referred to as "memory wear". The wear begins to deteriorate the integrity of the memory until it is becoming unusable in the end.

MLC technology in general has a limit of 3000 to 5000 P/E cycles per flash block specified by a FLASH manufacturers (https://en.wikipedia.org/wiki/Write_amplification). The limit per block makes a NAND-flash endurance directly dependent on its overall size, so the bigger the more blocks,  the better. An auto-wear leveling mechanism in the card's memory controller ensures the next erase/program cycle is performed on another flash block and hence distributes them evenly across the medium.

10 years life time in theory: There is a lifetime calculator available (from Toshiba) estimating the expected NAND flash life time. With netPI's 8GB @ 3000 P/E cycles it outputs a ratio of 1650 MBytes/day (chunks of 1000 x 1,65MB) you may write to the SD card to guarantee a 10 years life. In total this is 1650MB x 365days x 10years = 6022500MB or 6022GB or 6 TB of data the SD card tolerates. An other calculation can be for example like 25000 times a write of 64KByte chunks per day.

30 years Life time in practice: We made tough tests with an SD card to check its endurance under real life conditions. We brought a card to its limits at a incredible rate of 450000MB/day and realized the first failure after writing 18TB of data. So in reality an SD card has a 3 times higher endurance compared to the very conservative value the calculator provides.

There are two methods to increase the durability:

  1. Increase the memory card size while the NAND technology remains the same (MLC). Rule of thumb: double size, double durability.
  2. Switch to memory cards based on a  different NAND technology. Type "pSLC" has roughly 6x higher durability, type "SLC" has 30x higher durability compared to MLC
... so keep an eye on your applications.
You never fail until you stop trying.“, Albert Einstein (1879 - 1955)

#2
If the endurance of netPI's standard 8GB micro SD card is not sufficient for a use case then of course we support OEMs with netPIs populated with different type of SD cards of type pSLC or SLC.

Just to give you a slight impression about pricing for an equivalent 8GB high endurance mirco SD card of type SLC you can follow this link to distributor Mouser at https://www2.mouser.com/ProductDetail/Sw...Cokg%3d%3d
showing you an industrial suited SFSD8192N1BM1MT-I-QG-221-STD from Swissbit at a price of $128 (instead of $10 a MLC card would cost typically)
You never fail until you stop trying.“, Albert Einstein (1879 - 1955)



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