SD Card Reliability

Hardware
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There are recommendations on this forum and elsewhere to avoid using SD cards because they are not reliable (e.g., they wear out).

Device manufacturers typically measure reliability, under ideal conditions, as meantime between failure (MTBF) for harddisks or the total number of write operations for SDs and SSDs. They also compete on other metrics including speed, storage capacity, price, size, etc. so you can usually find this information if you search for it.

SD cards may not be able to do as many write operations as an SSD or harddisk but that does not mean they will fail sooner or be inappropriate for a specific application. I’m guessing that some (most?) media fail for reasons other than reaching their write operation limits or MTBF (e.g., file system corruption, environmental factors, user error, etc.). Also, comparing MTBF to write operation limits should be done based on individual application requirements.

It is acceptable, even desirable, to use an SD card for HA under the right circumstances.

So, my personal experience my be anecdotal; but, it is a real-world example. I have been rotating monthly through a set of four identical 32gb SanDisk A1 SD cards for approximately four years. I have a modest home automation setup (timed events and event driven automations). All automation, user interface, and mobile app response times are sub-second. Log and history data have default retention (I have history data over a year old). Disk space usage is stable at 22%. My RP4 is on a UPS (along with all my networking gear). Backups, upgrades, testing, etc. (in that order) are done monthly. Scheduled downtime has no impact on my family because my devices will work manually without HA.

I have not had a SD card fail yet.

But, if the SD card fails, I would be up and running on the backup SD card in the time it takes me to swap cards and start HA. I would lose at most 30 days of data which is ok for me but I could potentially recover more since I use the Google Drive Backup addon on a weekly schedule.

SD cards meet my requirements:

  1. Simple compared to an external SSD or disk drive (no extra cables, USB hubs or power supplies - potential points of failure)
  2. Cheap (currently $9.00 USD)
  3. Easily obtainable
  4. Sufficient performance and storage for my needs
  5. Fast recovery from backup.

Storage media has a finite life and predicting a failure can be difficult or impossible. It’s prudent to have backups. But a backup may be useless unless you prove (through testing) that it can be successfully used for recovery. Have a backup and test your recovery BEFORE you need it.

There are far too many “help - my system died” and “my backup doesn’t work” posts. The “don’t use SD cards” posts are misleading if reliable backups exist.

2 Likes
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Well said. I think sometimes the loudest messages here are the most extreme, asserting absolutes like “never use an SD card.”

My experience is similar to yours. 5 years now on my RPi 3B+ with an SD card matching the recommended specs. It rarely breaks single-digit CPU utilization or 50% drive utilization. Good response time. What’s not to like?

I have a backup SD card ready to go. I limit my Recorder writes by excluding the most spammy entities. I only do full HA backups monthly, when I do my regular version updates. In between I do regular backups of the config directory by reading from the SD card to my NAS. That doesn’t do any writes to the SD card, the way the HA backup does. Note that all the backup add-ons still create the backup on the SD card, then copy it elsewhere.

I imagine you could kill an SD card with HA if you don’t take any of this into consideration, or go wild with write-intensive functionality. But that doesn’t mean no-one should ever use one.

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I’d assume an sd card card designed for extreme ir cctv use would survive. I’d of thought cctv would nail it harder than ha?

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True. The Samsung Pro Extreme SD is designed specifically for that. I’m sure there are others.