the conpany i work for is making a proyect, we made Modbus RTU connection using raspberry pi 3 as a gateway, and saving the data to Mysql. this proyect have to be 24/7 and running forever, im wondering what will be the best SD? or should i use USB? or a HDD? also, about the power supply, what could be the best for this proyect?

1 Answer 1


Consider using externally powered SSD or spinning disks (depending on how much data storage is required). Have a look at external 5.25” drives in enclosures with good reviews. I would personally use a Synology Diskstation, which will you upload backups to a RAID1 mirror on your LAN.

You should script a full backup (with for example rsync -au /path1/source /path2/destination) to run daily, at 1AM, or whenever load is expected to be minimal.

If using flash memory locally on the Pi, leave 10-20% of space unallocated for TRIM. Gparted will be useful for you to do this.

  • thanks for replying, rigth now in this project the data has been saved in a PC SERVER, connected by LAN, so i think Synology its too much, raspberry rigth now is just for take the data from modbus RTU RS-485 but not for saving that data, my question about SSD or HDD, is beacuse the 24/7 working, not for the size of the data that im gonna save. can you explain me about the back up a little bit please. Commented May 10, 2018 at 17:39
  • @FreddyAlexSaavedra What type of backup? To USB? Use an rsync cronjob to copy to folders which are named after date... YYYYMMDD. Use ext4 filesystem. Just leave the thumbdrive in the Pi, replace it when it’s full.
    – user2497
    Commented May 10, 2018 at 20:23
  • oh, i understand now, thanks mate! but its ok, because im using only raspberry to read data, the PC SERVER is the one who save it, so the raspberry is never gonna be full. thanks so much for your help... Commented May 10, 2018 at 20:50
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    hahaha its okay mate, in this app yes actually we have 12 industrial devices, but the project for our client its kinda "big" so we dont "care" about how many raspberry we buy, so basically we are using 12 raspberry for 12 devices, all the 12 raspberry are connect with the normal ethernet cable. but the raspberry and the industrial devices are like in the same panel, so rigth now is one node for each raspberry for RTU-485 Modbus, and 12 Nodes Ethernet connection for the PC-SERVER (SQL SERVER). Commented May 17, 2018 at 22:30
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    we are not using any resistor, and we have no problem with the "GND" we are using only Modbus Protocol 485, 2 wires A and B , but we tried in both occation and works fine sharing GND and not sharing. Commented May 17, 2018 at 22:34

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