time dd if=/dev/zero of=zerofile bs=1M count=2048 conv=fdatasync,notrunc
2048+0 records in
2048+0 records out
2147483648 bytes (2.1 GB) copied, 28.728 s, 74.8 MB/s

real    0m28.732s
user    0m0.004s
sys     0m23.600s

time dd if=/dev/zero of=zerofile bs=1M count=6144 conv=fdatasync,notrunc
6144+0 records in
6144+0 records out
6442450944 bytes (6.4 GB) copied, 196.618 s, 32.8 MB/s

real    3m16.622s
user    0m0.012s
sys     0m27.726s

Bleh, sorry for so many posts.  I ran the same DD test on my OS disk that
is on the same controller as 4 of the RAID disks above.  It did much
better although that drive is slower than the ones that belong to the
RAID.

time dd if=/dev/zero of=zerofile bs=1M count=6144 conv=fdatasync,notrunc
6144+0 records in
6144+0 records out
6442450944 bytes (6.4 GB) copied, 109.823 s, 58.7 MB/s

real    1m49.827s
user    0m0.014s
sys     0m20.965s



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