In the last article, I went over my decisions about the hardware I wanted to use to build a cheap home NAS. Here I will go over the software and configuration to get everything working.

Once all the parts came in, it was time to get going and configure everything. First, though, I would like to talk about SD cards, and why I feel they are the one major flaw with the Raspberry Pi series.

Conceptually, SD cards are a great thing. They come in different sizes and can store multiple gigabytes of data on them. They are used in everything from cell phones to digital cameras to computers. You are probably using one daily in a device without even knowing it.

You might think there are hundreds of companies making them, and you would be wrong. See, as with many things, a few companies actually make the physical cards and then a lot of other companies will buy and re-brand them. The companies that slap their logo on these cards do not care whether they buy quality card stock as long as it is cheap. So what we end up with is a situation where you can by two of the same “type” of SD card and physically they could be quite different from each other.

You also may not realize that SD cards are just as capable of developing bad sectors as your physical hard drive is. Some cards have a smart enough controller built-in that will automatically remap bad sectors to other good spaces on the card like SMART does with hard drives. Many others do not and have a “dumb” controller that does the bare minimum to make the device work.

The reality with SD cards is that expecting them to “just work” is about as safe as playing Russian roulette with all six cylinders loaded. Just as with hard drives, your SD WILL fail. Unlike hard drives, your SD may or may not be able to take care of problems on its own. And with the wild west of the cards, well, your best bet is to never trust that data on them is safe.

At my previous job I spent a lot of time dealing with SD cards and learning how to deal with their various issues. Often we would have random problems come up that could not be explained, only to find out that the SD card had developed issues that needed to be corrected to return things to normal. What I found out after looking at the low level portions of the card and a lot of reading has made me rethink trusting these devices for long term storage and use. The Pi will be running an operating system off of the SD, so you can expect a lot of reads and writes being done to it. This will speed up the development of bad sectors on the device and reduce its operating lifetime.

There are a few things you can do to help things. Before you even start to install software for your Pi, I highly recommend that you do the check the physical surface of the SD before you use it, even if it is new out of the package. I’m writing this from a Linux perspective, but the same information applies to Windows or even Mac OS as well. As usual, your mileage may vary. Doing this could cause you to lose data and make dogs and cats live together in a dystopian future. This will take some extra time, but I firmly believe it is worth it.

Plug the SD into your computer and identify what device it is assigned. I will leave it up to you to web search this for bonus points. First thing I recommend is using the dd command to write random data to the entire device. If the SD card has an intelligent controller, this will help it to determine if there are any bad sectors and remap them before you put Linux on it for the Pi. Even without an intelligent controller, initially writing to it can help find spots that may be bad or trigger marginal sectors to go bad. Run a command similar to:

dd if=/dev/random of=/your/sd/device bs=8M

This command will write a random value to each byte on your SD card. Once this is done, the next thing I recommend is format the SD and check for bad sectors while formatting. This can be done with something along the lines of:

mkfs.ext4 -cc /your/sd/device

This command will put a file system on the SD and do a read/write test while formatting it. Along with the dd command, this should bang on the physical surface of the card enough to find any initial bad sectors that could already be there.

That is it for this installment. Now that my soapbox is over, next time we will talk installing software and configuring the Pi to be a NAS.