If I do:
# dd if=/dev/zero of=/dev/md0p1 bs=8M
then iostat -m 5 says:
avg-cpu: %user %nice %system %iowait %steal %idle
0.00 0.00 26.88 35.27 0.00 37.85
Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
sdb 265.20 1.16 54.79 5 273
sdc 266.20 1.47 54.73 7 273
sdd 264.20 1.38 54.54 6 272
sdf 286.00 1.84 54.74 9 273
sde 266.60 1.04 54.75 5 273
sdg 265.00 1.02 54.74 5 273
md0 55808.00 0.00 218.00 0 1090
If I do:
# dd if=/dev/zero of=/dev/md0p1 bs=8M oflag=direct
then iostat -m 5 says:
avg-cpu: %user %nice %system %iowait %steal %idle
0.00 0.00 11.70 12.94 0.00 75.36
Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
sdb 831.00 8.58 30.42 42 152
sdc 832.80 8.05 29.99 40 149
sdd 832.00 9.10 29.78 45 148
sdf 838.40 9.11 29.72 45 148
sde 828.80 7.91 29.79 39 148
sdg 850.80 8.00 30.18 40 150
md0 1012.60 0.00 101.27 0 506
It looks like md isn't recognizing that I'm writing whole stripes when
I'm in O_DIRECT mode.
--Andy
--
Andy Lutomirski
AMA Capital Management, LLC
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