Could you tell me how to purge, clear, the USB disk read/write cache with command line on ssh session.
If you are going to extract the drive, the "mount" command will not finish untill all pending writes have finished.
Otherwise, there exists the "fsync" system call, and the "sync" command.
Not exactly my purpose;
After write, I want to purge the cache to measure the read time with disk access.
I don't think the sync/fsync will purge the RAM cache I think it will copy the data in the disk.
Yes, fsync will force pending writes to the drive, but it will also retain the cache in RAM. I do not know of a specific command to delete the cache, but unmounting the drive will surely have that effect.
I found it here
It's working for Openwrt
free -m total used free shared buff/cache available Mem: 511968 185620 28996 332 297352 285400 Swap: 0 0 0 ~# sync; echo 3 > /proc/sys/vm/drop_caches ~# free -m total used free shared buff/cache available Mem: 511968 182460 323880 332 5628 304768 Swap: 0 0 0
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