UFS Large file process slows disk access


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I'm running a 10.2 machine. Works fine, pretty responsive. However, if I'm doing a large file manipulation (not just, but especially pg_dump(1)), disk access for other things pretty much stops. I've played around with scheduler choice and preemption and they seem to be no silver bullet. I have set
sysctl vfs.read_max=256 on this 8GB machine.

Other than nice-ing things is there a setting I can monkey with here?

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Insert a GEOM scheduler instance between the disk providers and their consumers. The GEOM scheduler stores no metadata on devices so you have to insert the scheduler instances yourself in /etc/rc.local:
sysctl -n kern.disks | xargs -n 1 gsched insert
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