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Archive for October 28th, 2015

SATA vs. USB Hard Drive Write Speeds

The stack of drives-to-be-scrubbed disgorged a pair of SATA drives, so I plugged one of them into an internal SATA port and unleashed dd on it:

time sudo dd if=/dev/urandom of=/dev/sdb bs=4096 count=10000
10000+0 records in
10000+0 records out
40960000 bytes (41 MB) copied, 4.19793 s, 9.8 MB/s

real	0m4.208s
user	0m0.004s
sys	0m2.880s

time sudo dd if=/dev/urandom of=/dev/sdb bs=1024 count=40000
40000+0 records in
40000+0 records out
40960000 bytes (41 MB) copied, 7.38392 s, 5.5 MB/s

real	0m7.394s
user	0m0.004s
sys	0m3.505s

time sudo dd if=/dev/urandom of=/dev/sdb bs=16384 count=2500
2500+0 records in
2500+0 records out
40960000 bytes (41 MB) copied, 4.2042 s, 9.7 MB/s

real	0m4.214s
user	0m0.000s
sys	0m2.880s

The timing for a few (tens of) thousand blocks comes out somewhat below the long-term average, which was the same 12 to 14 MB/s produced by the USB 2.0 adapter. It just doesn’t get any better than that, mostly due to rotational delays.

In round numbers, that’s 40 to 50 GB/h, so it’s best to start scrubbing those terabyte drives early in the day…

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