Am 27.01.20 um 21:42 schrieb deloptes:
It depents on the Ports, ho they are connected to the host. A USB2 host has ma speed of 480 Mbit/s (60 MByte/s), if both HDD's/ USB Ports are connected to the same USB host it's a half of that, minus overhead. Many USB to SATA adapter has a very poor performence, thats right, but this depents on the adapter chip.basti wrote:Yes a rpi can run software raid with mdadm. In this case I would use a rpi4b with USB3 and USB to SATA adapter but be aware that the rpi is at the moment not fully supportet by debian (https://github.com/lategoodbye/rpi-zero/issues/43). If raspian is good enough for your needs it would be an option. With the restrictions I explained before.I tried many years ago SATA adapter with USB2 and the performance was very poor. Might be better with USB3 though, but I am still not convinced. I saw some time ago there was extention board with SATA 2 or 4, which was promising. Interesting to know if someone have used such thing with debian.
I have test a single HDD drive with sata to USB3 adapter on the rpi4 and get transfer rates round about 90-100 MB/s so a RAID with 2 drives can have write speeds about a half of them and read speed even more I guess.
Perhaps with a SSD it can be more, USB3 specs are round about 600 MB/s. The gigabit Ethernet has 125 MB/s in theory so it would be still enough. But I have not test this and this is not the topic there.