- From: Andrew Protasov <andrew.protasov@xxxxxxxxx>
- Date: Fri, 4 May 2012 11:02:50 -0700 (PDT)
Did anybody ever push DBWR to reach max disk write speed?
I have /dev/md0, /dev/md1 and /dev/md2 with identical configuration:
raid1 on 2 3TB hdd, 6 hdd total. I can reach 180MB/sec write speed on
each of them running 3 bonnie++ concurrently. Filesystem is xfs on all
Data goes on /dev/md0, redo on /dev/md1 and undo on /dev/md2.
Execute insert /*+ append */ and write speed on /dev/md0 goes to
150-160MB/sec as seen by iostat. Good, this is close. Obviously
nothing goes to /dev/md1 and /dev/md2.
Execute insert (no append) and dbwr write speed on /dev/md0 is 0MB/sec
and lgwr on /dev/md1 reaches 130MB/sec until db block buffers are
full. Then dbwr speed is only 50MB/sec and it also holding back lgwr
To me it looks like dbwr is incapable of writing more then 50MB/sec
and holding everything back.
I would expect write speed on /dev/md0 and /dev/md1 to be 180/180 MB/
sec, not 50/50 MB/sec.
Adding >1 db writers or >1 slaves does not change this picture. Async
io is on, direct io is on. DB block buffers 4GB. Test table size
Config: fedora 16 64bit, oracle 11.2, xfs, 32GB ram, AMD FX-8120.
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