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To: Alexander Motin <mav@FreeBSD.org>
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i routinely put
options         MAXPHYS=2097152

on my servers. no problems, except MUCH enhanced performance on large 
files. with UFS.

SOME SSDs (few) doesn't work properly with >1MB requests.

no idea about ZFS.

with NFS do not ever expect good performance with it's sync mode. if you 
like to take a risk add
vfs.nfsd.async=1

to sysctl.conf


unless your NFS clients depend on forced syncs, the risk is actually no 
higher that running normal UFS filesystem locally. And performance is 
excellent.