really slow RMAN backups
This was just passed to me, but I thought I'd check with the group to
see if anyone else has experienced this slowness.
- From: Steve Perry <sperry@xxxxxxxxxxx>
- To: ORACLE-L <oracle-l@xxxxxxxxxxxxx>
- Date: Mon, 21 Aug 2006 17:08:06 -0500
I don't have any experience with netapp and want to see if there are
some known issues with it.
RMAN backups (2 tape channels) take forever on this system. forever
means 20+ hours.
the view v$backup_sync_io shows the effective bytes per second at 2
or 3 MB per second. nothing above 5MB per second.
v$backup_async_io doesnt' show anything.
500GB database on a netapp filer (40+ disks, don't know the model)
2 - node RAC EE cluster
1 GB swap
600 MB SGA (small and uses the automatic memory management)
flash recovery area is on
DG is setup for 2 different databases
mtu sizes of all NICs are set to 1500 (since it's netapp, they might
prefer something else)
legato is the media manager
I looked at the init.ora settings and besides the small sga,
disk_asynch_io = false
filesystemio_option = directIO
large_pool_size = 52M
I don't know why they chose directio (1 dbwr) instead of async. they
may not have anything to do with it, but it's the first time I saw
them set on a RAC database.
I ran an awr report and "RMAN backup & recovery I/O" was the top
waiter with an avg wait of 134 ms. the class is "system io".
other things are an index with 19 million get buffs during 2 hour
I see a few slow access times 300ms avg. read time, but there are
only 200 or so reads against it. Most of the access times are less
I don't know if the problem is contention with other jobs, config
parameter or hardware.
I checked a similar system (db ver, 2 node rac, asm) that gets
80-90MB per second for it's backup.
it's on the SAN and uses async.
I haven't looked at the awr report from it.
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