disk bandwidth

Sequential bandwidth across an entire disk (ST3500514NS)


diskgraph.pdf
diskbench.sh

Random 8MB Segment bandwidth (ST3500514NS)

diskbw.c

"Optimal" read/write bandwidths are 129.85MB/s and 130.5MB/s, respectively. This represents the best the disk can do anywhere, so they're really optimal numbers for the lowest sectors (outer-most tracks of the disk). Note that these are with write caching on, which increases sequential write bandwidth by about 10-15%.

Disk Range ??(first seg, last seg)

Avg Read BW

Read PCT Optimal

Avg Write BW (wr cache on, off)

Write PCT Optimal

Whole disk (0-58000)

87MB/s

67%

71.8MB/s, 85.7MB/s

55%, 66%

First half (0-29000)

103.5MB/s

79.7%

80MB/s, 102.7MB/s

61%, 79%

First quarter (0-14500)

107.9MB/s

83.1%

90.4MB/s, 107.6MB/s

69%, 82%

First 1GB (0-120)

114.6MB/s

88.3%

102.7MB/s, 114MB/s

79%, 87%

Note that there appears to be a significant random access write penality when the disk write cache is enabled (hdparm -W1 /dev/foo).

Cluster Hard Disk Bandwidth August 2011 (rc01-rc60)

Putting this data up in case we plug our disks back in and want to see if performance has changed much over time.

Note 'rcXX-2' indicates the second disk. rc01-rc40 have a WD2503ABYX enterprise disk in the first slot and a desktop Seagate ST3500418AS in the second. rc41-rc60 have only WD disks (which is pretty obvious in the fans high graph).

Fans at normal speed (typical vibration):

Fans at highest speed: