Difference between revisions of "ZFS on high latency devices"

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IO prioritization: assume SRmax is the highest max (it usually will be).  If not, find a compromise value for it so that
IO prioritization: assume SRmax is the highest max (it usually will be).  If not, find a compromise value for it so that
the other max numbers are within 4 threads of SRmax
the other max numbers are within 4 threads of SRmax.  This is an old trick from Sun, set as follows;
 
* SR: 4 - SRmax
* SW: SRmax/2 - SRmax
* AR 2 - ARmax
* AW 2 - AWmax
* Scrub 0 - 1
* VDEV max: SRmax * 1.25
 
These values are adjustable but are designed for SRmax, ARmax and AWmax to all be relatively high without fighting
with each other.  When SR or SW is saturated, they share SRmax worth of threads roughly equally, and allow AR and AW
to share the remaining 20%.  The low value for SRmin keeps sync reads from dominating other I/O.


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