Very low disk performance on 5.x

[Martin Nilsson]

Petri Helenius wrote:
> I noticed that changing vfs.read_max from the default 8 to 16 has a 
> dramatic effect on sequential read performance. Increasing it further 
> did not have measurable effect.

Increasing MAXPHYS in sys/param.h from 128k to 1M increased sequential 
read thruput on my MegaRAID 1600 from 100MB/s to 190MB/s measured on 5.4

#RAID0 7*36GB MegaRAID 1600 MAXPHYS=1M
t125# dd if=/dev/amrd0 of=/dev/null bs=1024k count=1024
1073741824 bytes transferred in 5.559722 secs (193128691 bytes/sec)

It had no effect on bonnie so the filesystem probaby never issues 
block-reads that large, I'll try the above sysctl.

190MB/s is pretty good considering that the card is in a ServerWorks LE 
chipped P3 and that the internal datapath on the Elite 1600 is only 
64-bit/33MHz.

/Martin