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RE: Oracle & SAN Experiences?

From: Mark Brooks <>
Date: Sun, 10 Nov 2002 23:38:41 -0800
Message-ID: <>

Guess I wasn't clear with my earlier post. Here is the information from the SA's when confronted with the results of some I/O tests.

Configuration on system 1 ( poor IO performance ):

Large filesystem --> device driver --> hardware controller --> SAN switch --> SAN Server

Configuration on system 2 ( better IO performance ):

filesystem1 --> device driver --


filesystem2 --> device driver --> hardware controller --> SAN switch --> SAN Server

filesystem3 --> device driver --

In configuration 1 the system was bottlenecked in the device driver, the SAN hardware was running fine.

In configuration 2 the system was able to spread IO over multiple device drivers and gave better performance.

Hope this clears things up. Might have been a deficiency in the volume manager software. Point I was trying to make was that when you switch to SAN storage you still have to be aware of the limitations of the host systems IO subsystems and look at tuning / configuration on both the SAN hardware and your host system.

-----Original Message-----

Sent: Saturday, November 09, 2002 3:19 PM To: Multiple recipients of list ORACLE-L

It would be extremely surprising if there was a static relationship between the number of file-systems and the number of I/O controllers used by each. Sounds more like a mis-configuration, a mis-interpretation of the symptoms, or (most likely) a cover-up story to redirect blame.

There is no awareness of controllers or other devices (other than logical volumes a.k.a. "raw" devices) in file-systems. This is a configuration issue for the SAN controller hardware/firmware/software, although I believe that the Veritas VxVM software can perform dynamic multi-pathing, so it could be performed at the LVM (logical volume manager) layer as well...

Load-balancing and failover amongst I/O controller devices is common in SAN environments. It doesn't make sense to allow $200.00 controller cards to be either a bottleneck or a single-point-of-failure in an I/O subsystem costing millions of dollars...

One observation I have made at sites running SAN storage for Oracle is a tendency for the SA's to present the disk to the database server as a small number of large filesystems. On some OS platforms this can create a bottleneck on the host as all data to this large filesystem is routed through a single device driver. Solution is to present more filesystems and therefore have more channels from the OS perspective to access the disk.
-----Original Message-----

Sent: Friday, November 08, 2002 6:59 AM
To: Multiple recipients of list ORACLE-L

The Sys. Admin. team wants to consolidate storage (and probably get a new toy too) on all of our servers, so they are evaluating a SAN (LSI Logic E4600). The DBA team is doing some research to determine the pros and cons of doing this, and I’d like to hear any of your experiences (good and bad) using SAN with Oracle.

My understanding is that all of our database servers would remain intact, but the attached disk storage would move into the SAN. So, we still have the Production, Test, and App. servers with their processors and memory, Oracle homes, etc. The SAN will hold database files from Production, Test, Apps., staging, ODS,data warehouse, etc.

Their arguments:
-the SAN is very scalable (500 GB – 40 TB)
-easy to manage disks in one central location
-fancy statistics collection on all SAN disks
-much higher throughput on the fiber SAN connections than with locally
attached disk arrays
-capable of using mixed RAID levels (0, 1, 1+0, 5, etc.)
-can partition sets of disks in the SAN for specific server access
-Snapshot backup capability is very fast in the SAN (much faster than
traditional Oracle backups)

DBA arguments:
-How will this affect database performance?
-What are the drawbacks, if any, with the pre-fetch of data performed by the
SAN (i.e., SAN cache)
-How tunable is the SAN
-Fast, small disks are better for performance and less wasted space than the
typical huge disks in a SAN (it’s possible to use smaller disks in the SAN)
-Prove it!

After reading the “Sane SAN” article and a case study about Volvo implementing a SAN, I believe it’s possible to have a great Oracle/SAN implementation if it’s setup correctly and tuned. Other resources that you can Google are “Using SVA SnapShot with Oracle”, “Performance Benchmark LSI Logic E4600 (STK D178)”, “SAN Storage for Open Systems Environments”, and of course check the OraFaq.

Thanks for sharing,

David Wagoner
Oracle DBA


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Author: Mark Brooks

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