Re: ASM of any significant value when switching to Direct NFS / NetApp / non-RAC?
- From: Austin Hackett <hacketta_57@xxxxxx>
- To: "Oracle-L@xxxxxxxxxxxxx" <Oracle-L@xxxxxxxxxxxxx>
- Date: Wed, 15 Aug 2012 21:51:54 +0100
Hi Dana
This info doesn't exactly relate to ASM, but I hopefully it'll be of
use to you in the future...
I've recently started a new role at shop that uses Linux, Direct NFS
and NetApp (no ASM) and as others have suggested, the solution does
have a number of nice management features.
However, I am finding the apparent lack of read and write latency
stats frustrating.
Something I'm currently looking into are occasional spikes in redo log
writes. I know these are happening because there are log write elapsed
warnings in the LGWR trace file. When these spikes occur, NetApp Ops
Manager reports 2 - 3 millisecond write latencies for the volume in
question.
What I'd like to be able to do is cross-check these warnings against
host-level io stats, but there seems to be no way of achieving this.
Using the standard Linux NFS client, iostat can show you the number of
reads, writes etc. but not latencies. With the 2.6.17 kernel it seems
that counters are available to report latency information, and there
are scripts like nfs-iostat.py out there which will display this
info:
http://git.linux-nfs.org/?p=steved/nfs-utils.git;a=blob;f=tools/nfs-iostat/nfs-iostat.py;h=9626d42609b9485c7fda0c9ef69d698f9fa929fd;hb=HEAD)
.
However, because Direct NFS bypasses the hosts NFS mount points
(oracle db processes mount the files directly), it's my understanding
the above tools won't include any operations performed by the Direct
NFS in their output. There is a post about this here:
http://glennfawcett.wordpress.com/2009/11/25/monitoring-direct-nfs-with-oracle-11g-and-solaris-pealing-back-the-layers-of-the-onion/
Now, whilst the v$dnfs_stats view does record the number of reads,
writes etc, it doesn't have any latency data. Which just leaves you
with usual v$ and AWR views like v$eventmetric, v$system_event etc.
And if you're trying to confirm the issue is at the host level and
not Oracle, this doesn't help you much. So, at the moment I'm missing
being able to run iostat and see svc_t and the like...
Incidentally, Glen Fawcett has nice script here for capturing v
$dnfs_stats output:
http://glennfawcett.wordpress.com/2010/02/18/simple-script-to-monitor-dnfs-activity
It's also worth being aware of bugs 13043012 and 13647945.
Hope that helps
Austin
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