Examples of good performance

When busy but not overloaded, iostat data for this system looks as follows:

    $ iostat 5    avg-cpu:  %user   %nice %system %iowait  %steal   %idle              18.54    0.00    9.45   23.49    0.15   48.38    Device     tps Blk_read/s  Blk_wrtn/s  Blk_read  Blk_wrtn    sdc1   1068.80       0.00    15740.80         0     78704    sdd1   1041.80       0.00    15459.20         0     77296    sde1   1028.00       0.00    15377.60         0     76888    md0    5969.20       0.00    47753.60         0    238768    sdf1    989.00       0.00    40449.60         0    202248  

The %iowait figure of 23% is high enough to know the disks are busy, but not completely saturated yet. This is showing 20 MB/s (40449.6 512-byte blocks per second) being written to the WAL and 24 MB/s to the entire database disk array, the latter of which is evenly split as almost 8 MB/s to each of the three drives.

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