SUMMARY: NFS mounting Oracle datafiles

From: Callum Hughes <>
Date: Thu Apr 04 2002 - 04:57:17 EST
Firstly, many thanks to the HUGE number of people who replied to my question
about NFS mounts of Oracle database files. The response was amazing and the
information was really useful. I received a great mix of "fors" and
"againsts" and it was a proper maelstrom of thought digesting each mail I
can tell you! One email would come in saying it was fine, another not, then
another not, then another fine and so on! 

In short, there are several key points that were raised by those
contributing, and I won't paste them all together as the email would be

But first, the thanks list...

Martin Hepworth
Tim Chapman
Kevin Buterbaugh
Marc Alvidrez
Brian McGraw
Gary Mulder
Justin Stringfellow
Michael Sullivan
Dylan Northrup
John Leadenham
Jeff Kennedy

Righty right... onto the good stuff... much plagiarising going on here! But
all done in the "best possible taste..."

Point 1: The information that I had from Oracle referred to older versions
of NFS which relied upon UDP. NFS3 now uses TCP and is since much more
reliable. However, NFS is much slower than SCSI and so for a busy database,
a Gb ethernet might be in order... 

Point 2: Oracle assumes that data is safe when it sends a write to disk but
NFS actually caches data first. If you lost the NFS server, you lose that
data. This was a major point for many people - if the Oracle instances are
on another server, then your database may get corrupted by some such event
happening and refuse to start back up once the NFS server is back up... 

Point 3: Oracle (allegedly) support NFS mounts but only when done through
"filers". These apparently rename the datafiles so that the database doesn't
come up without the DBA if it can't assure the state of the files.  A pretty
good solution for the problem outlined in Point 2!!! Brian kindly provided
this URL for approved vendors...

Point 4: The speed of your network connection will effect the stability of
your setup. The speed with which Oracle can write to the storage is central
to how efficient the transfers will be. The benefits of NFS is that it's a
cheaper (possibly) option that an attached array but, a lot slower. Gary
provided these stats: "NFS performance is extremely poor as compared to
SCSI. Gigabit ethernet might get you 50MB/sec due to all of the TCP/IP and
NFS overhead. Properly configured RAID should provide you 80+MB/sec."

To summarise: it can be done but is not advisable unless using a Netapp
filer. The risk of losing the NFS server needs to be considered high no
matter what server you're using. Oracles data was out of date (the stuff I
had) regarding NFS which is worth noting, and they do claim to support this
config when used with filers. 

In theory, you can do this without filers, but in practice, it's not
something that you would want to do without them! 

As a side note, the customer rejected the solution proposed but not on the
grounds that the NFS solution may be risky, but that they would RATHER stay
with Data General servers... 

Who says life is dull?

Thanks to all!

Callum A. Hughes
Unix Systems Engineer
Securicor Information Systems

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Received on Thu Apr 4 04:01:27 2002

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