Would not call myself an expert, but I run all
of my file system (Debian) on an external drive. I have also kept the Ubuntu (upgraded, ubifs) in the flash. One upgraded kernel is in nand flash and will boot for either distribution with a small change to U-Boot variables.
By the way, my external drive is a 64 GB SSD, power from the Plug. The Plug's internal power supply was removed and replaced by a 5 V, switching, 2.5 A external unit.
My reasoning for this configuration:
- The machine is to be used for a specific purpose, not just for testing -- Want it to last as long as possible.
- Running an operating system in it, the internal nand flash will wear out over time. The flash is difficult to replace.
- The external drive can be replaced fairly easily.
- Using the external drive for all the file system means the flash is only written to when upgrading the kernel or doing maintenance on the external drive. With this little usage, it should last for years.
- Using an SSD to reduce power consumption. It is mounted as ext4, with the discard option, so TRIM will work. The drive is also formatted as a single unit (/dev/sda not /dev/sda?) to keep the erase blocks aligned.
- With that set-up, as long as there is plenty of free space on the drive, it should operate efficiently for a long time.
- The SD card slot remains open to perform backups.
- Had planned to us an SD Card as the device for the file system. But with reports of problems and fears of accidentally harming the file system by bumping the card, rather only use the SD when doing maintenance.