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❤️ SD Card Health

Overview​

SD cards in industrial and embedded systems endure significant wear due to continuous read/write operations. Monitoring their health can help predict failures and extend their lifespan. This guide provides a Dockerized approach using mmc-utils, and explores native Linux tools like iostat and /proc/diskstats for tracking SD card wear and performance.

1️⃣ Setting Up mmc-utils in Docker​

Dockerfile for mmc-utils​

This Dockerfile:

  1. Clones the official mmc-utils repository.
  2. Clones the transcend repository including patches to source files that make it possible to fetch SMART information from transcend SD Cards.
  3. Overwrites the files in the official mmc-utils repository with the ones coming from Transcend.
  4. Builds the modified mmc-utils.
  5. Allows running the tool on host devices.
# Stage 1: Build the binary
FROM debian:bookworm-slim AS build

RUN apt-get update && apt-get install -y \
    git build-essential sparse \
    && rm -rf /var/lib/apt/lists/*

WORKDIR /app

RUN git clone https://kernel.googlesource.com/pub/scm/utils/mmc/mmc-utils
RUN git clone https://github.com/transcend-information/RaspberryPi_NVIDIAJetson-SDcard-SMARTQuery.git transcend-patches

RUN cp transcend-patches/mmc-utils/lsmmc.c mmc-utils/ && \
    cp transcend-patches/mmc-utils/mmc.c mmc-utils/ && \
    cp transcend-patches/mmc-utils/mmc.h mmc-utils/ && \
    cp transcend-patches/mmc-utils/mmc_cmds.c mmc-utils/ && \
    cp transcend-patches/mmc-utils/mmc_cmds.h mmc-utils/

WORKDIR /app/mmc-utils
RUN make

# Runtime stage: copy only the binary into a minimal environment
FROM debian:bookworm-slim

# Create directory for binary
WORKDIR /app

# Copy compiled binary from previous stage
COPY --from=0 /app/mmc-utils/mmc .

ENTRYPOINT ["./mmc"]

Building & Running the Container​

1️⃣ Build the Docker Image​

docker build -t mmc-utils .

2️⃣ Run the Container with Access to the SD Card​

docker run --rm --privileged -v /dev:/dev mmc-utils smart /dev/mmcblk1

(Replace /dev/mmcblk1 with your actual SD card device path.)

Monitoring SD Card Health with mmc-utils​

Check SMART Info​

docker run --rm --privileged -v /dev:/dev mmc-utils smart /dev/mmcblk1

Check SD Card Health​

docker run --rm --privileged -v /dev:/dev mmc-utils health /dev/mmcblk1

2️⃣ Monitoring SD Card Write Activity with iostat​

iostat provides real-time disk usage and I/O statistics.

Installing iostat (if not installed)​

sudo apt-get install sysstat

Basic Usage​

iostat -d -k 1 1
  • -d: Show disk statistics.
  • -k: Display values in KB (kilobytes).
  • 1 1: Take one measurement, wait one second, and print the result.

Example Output:

Device       tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
mmcblk1      12.0         0.0       1536.0         0       1536

📌 Key Metrics:

  • tps = Transfers per second.
  • kB_wrtn/s = KB written per second.
  • kB_wrtn = Total KB written since system boot.

Continuous Monitoring​

iostat -d -k 10

📌 This updates every 10 seconds.

3️⃣ Deep Dive: Visualizing Disk Statistics (/proc/diskstats)​

Linux provides detailed disk write statistics through the /proc/diskstats file. Here's a clearer and more interactive approach:

🔍 Check Disk Write Stats​

Quickly view statistics for your disk (e.g., mmcblk1):

cat /proc/diskstats | grep mmcblk1

Example Output:

179       0 mmcblk1 33890 8762 2892906 110522 22176313 8542353 249743440 47112865 0 49371376 47569059 6702 9 104127704 345671 0 0

📋 Important Metrics​

MetricField #Example ValueDescription
📝 Sectors Written10249743440Total sectors written since boot.
⏱️ Write Time (ms)1147112865Total milliseconds spent writing.

🧮 Calculate Data Written (One-liner)​

Each sector is 512 bytes. Here's a simple one-liner to display sectors written directly in MB:

echo "$(( $(awk '$3=="mmcblk1"{print $10}' /proc/diskstats) * 512 / 1024 / 1024 )) MB written"

📌 This outputs data written directly in MB.

🚀 Conclusion & Recommendations​

  • ✅ Use mmc-utils in Docker to assess SD card health (SMART & erase cycles).
  • ✅ Monitor real-time write activity with tools like iostat.
  • ✅ Analyze historical data precisely using /proc/diskstats.