SD card read speed on Duet 3 Mini 5+ lower than write?
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Hi everyone, I was wondering if anyone else was experiencing this. I am using the SD card that was provided with my Duet 3 Mini 5+. When I test it, it seems that the write speed is faster than the read speed?
M122 P104 S25 Testing SD card write speed... SD write speed for 25.0Mbyte file was 3.74Mbytes/sec Testing SD card read speed... SD read speed for 25.0Mbyte file was 0.64Mbytes/sec M122 ... === Storage === Free file entries: 10 SD card 0 detected, interface speed: 22.5MBytes/sec SD card longest read time 4.3ms, write time 166.2ms, max retries 0 ...What kinds of speeds are you all experiencing? I'm running 3.4.0beta5.
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Your SD socket might be failing. Is everything working correctly?
There are several comments about read/write speeds here:
https://duet3d.dozuki.com/Wiki/SD_Card#Section_SD_Card -
@alex-cr Everything seems to be working to the best of my knowledge.
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@j3d I can copy that with RRF3.3 on a STM board. (Duet2 is the same 1:3 factor between read/write)
The reason might be, that reading data always loops through the gcode parser/planner? Just guessing...Did you try to upload/download a huge file through DWC and count seconds? IMHO, that should be more equal.
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@j3d the reason is that we want file uploads to be as fast as possible, and SD cards prefer large block writes; so RRF uses a 8K write buffer. In contrast, it's rare to download files from the Duet, and other file reads from the SD card don't need large blocks of data in one go; so RRF uses much smaller read buffers.
