ATTO Technology R30F Installation And Operation Manual page 19

A spike in the graph indicates a disk read or write
to or from the system cache or the cache
incorporated in the disk being tested. The top of
this spike is normally the peak read or write value.
The peak value is also commonly referred to as
the burst transfer rate.
When the system disk cache is turned on, the
performance of a volume may appear to exceed
the maximum performance of the bus because
sometimes Data are being transferred to or from
the System Disk Cache (system RAM) rather than
to or from the disk being tested.
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