Run the dd command in CentOS to test the read/write speed of the USB flash disk.

1. dd command description: if = input file, of = output file, ibs = number of bytes read at a time, obs = number of bytes written at a time, bs = set the number of bytes read and write at a time, skip = number of bs skipped, count = number of copies 2. use/dev/null and/dev/zero1. to regard/dev/null as & quot; Black Hole & quot;. it is equivalent to a write-only file, and all content written to it will be lost forever.

1. brief description of the dd command:

If = input file, of = output file, ibs = number of bytes read at a time, obs = number of bytes written at a time, bs = set the number of bytes read and write at a time, skip = number of bs skipped, count = number of copies

2. use/dev/null and/dev/zero

1. think of/dev/null as a "black hole". it is equivalent to writing only files, and all the content written to it will be lost forever.

2./dev/zero is a pseudo file, but it actually produces continuous null streams.

3. test the read/write speed of the USB flash drive.

# Switch to the USB flash drive directory and test the write speed # dd if =/dev/zero of =. /largefile bs = 8 k count = 1000010000 + 0 records in10000 + 0 records out81920000 bytes (82 MB) copied, 11.0626 s, 7.4 MB/s # Test read speed (clear cache) # sudo sh-c "sync & echo 3>/proc/sys/vm/drop_caches" # dd if =. /largefile of =/dev/null bs = 8k8000 + 0 records in8000 + 0 records out65536000 bytes (66 MB) copied, 2.90366 s, 22.6 MB/s