Reliable SD Cards

Question

My notebook (T560) only supports one harddrive and I would like to expand it by a 256GB SD card for things like backups. So I surfed the net for a while and noticed that up to 10% (felt 10%) of sd card users have problems with failure of them. So I would like to ask if it is a bad idea to go this way.

Are there any "attributes" determining the quality of a sd card based on the failure rate? What else do I need to take into concern?

I am a Linux user so I would like to use a filesystem like ext4 (or later btrfs) don't know if there can be problems concering the support of such FS.

PS.: I always appreciate it if you fix my English.

Answer 1

SD cards aren't restricted to some filesystems. SD card is just a memory that can hold a predetermined amount of bytes. It doesn't know or care what a filesystem is.

Unfortunately, that's the end of good news I have for you.

1. SD cards are quite fragile. They are prone to mechanical failures. Full-sized cards are a bit more resilient than microSD, but they definitely can't be considered reliable.

2. SD cards can be slow. Regular, cheap SDs are rated up to 10 MB/s. To give you a point of reference, typical laptop HDDs reach about 80 MB/s for sequential access (for non-sequential access SDs can be faster). UHS and Video SDs can reach about 90 MB/s if your SD card reader supports these speeds. Consumer SSDs reach 500 MB/s.

3. SD cards have limited lifespan and won't warn you before they die. Flash memory wears out pretty quickly. I've heard of SD cards dying after 2-3 months.

4. Using non-standard filesystems will limit compatibility. Default filesystems are: FAT16 for regular SD (up to 2 GB), FAT32 for SDHC (up to 32 GB), exFAT for SDXC (≥ 64 GB). Other filesystems aren't guaranteed to be supported. If the card contains a partition table, Windows will only recognize its first partition, so formatting as a superfloppy is preferred.

5. Using a filesystem that isn't flash-optimized (like ext3, ext4 or Btrfs) will shorten card's lifespan even more (see #3). If you really need a Linux-native filesystem, I'd recommend ext2 due to its lack of journaling. If you don't care about compatibility, consider F2FS - exotic, but designed specifically for flash storage.

These points (mostly #1, #3 and #5) make SD cards rather unsuitable for backups and storage, they are just too unreliable.

Moreover, anything that's in the same device as your original data is not a backup. Specifically, second built-in hard drive or an SD card is not a backup.

• When your laptop is stolen, your data is lost.
• When your laptop is left in a building on fire, your data is lost.
• When your laptop suffers a critical hardware failure and fries its components, your data is lost.

A real backup protects against all of these scenarios. For real, reliable backups, use the 3-2-1 rule: keep three copies of your data, use at least two physical storage media and keep one in separate physical location.

Answer 2

Using an SD card as a backup drive is quite safe. SD cards are prepared for thousands of write cycles (they were designed for saving photos over and over again).

I have been using an old 8GB SD card as my boot drive (running Ubuntu) for years on a Intel Classmate and haven't lost anything.

The only advice is to buy from a known brand. Since you will be using it for backup the speed is not critical.

In any case even if you use it for backup only, the failure rate is not that important since your original files are on the laptop. If a backup fails then you know it's time to replace the SD card.