Ah, I'm probably good then, this was sustained write during preclear.
For giggles, here's some other metrics:
root@isak:/boot# hdparm -Tt /dev/sdf
/dev/sdf:
Timing cached reads: 2566 MB in 2.00 seconds = 1283.38 MB/sec
Timing buffered disk reads: 788 MB in 3.00 seconds = 262.24 MB/sec
root@isak:/boot# dd if=/dev/zero of=/dev/sdf bs=8k count=10k
10240+0 records in
10240+0 records out
83886080 bytes (84 MB) copied, 0.460711 s, 182 MB/s