Multiple VS. Single RAID volume with Oracle?

[Greg OBarr]

Cool, so just separate LUNS for Oracle datafiles and archive/redo/backup. That was the minimum I wanted to do. But apparently, it's better to stripe all the Oracle data across 1 LUN rather than 2 separate ones. At a minimum, I didn't want the disks competing for Oracle I/O and writing backups, redo, and archive logs out to the same disks. I should see a good performance increase by

A) going from 10K disks to 15K disks
B) going from 128Mb array controller cache
to 1Gb cache
C) going from RAID 5 to RAID 1+0

Considering that I have A and B no matter what, just by upgrading the hardware, I'm not sure the payoff would be worth the wasted disk space of going from RAID 5 to 1+0.

Anybody done any comparisons on the effect of RAID 5 vx. Raid 1+0 on Oracle OLTP using a disk array with very good I/O performance? (the vendor claims there is 10% or less performance impact using RAID 5 on their arrays with Oracle)

[Greg OBarr]

Geoff, others, please elaborate on convosync, etc in respect to LV/VG configuration.

We are mounting the filesystems now with only "-o rw, suid" options. I recall hearing that some benefit could be gained by using convosync in the mount options, but I wasn't aware that this had anything to do with the LV/VG configuration. I just thought you added "convosync" to the mount options. Obviously, I haven't tried this yet, but what information am I missing here?

[Todd McDaniel_1]

Greg,

This page will give you a good idea of mincache and convosync both of which are very good for attached Oracle filesystems.

http://uw713doc.sco.com/en/ODM_FSadmin/fssag-8.html


NOT using the unix system cache is advantageous b/c you dont tie up system resources handling I/O and logging etc...I use the following on my Oracle EMC mounted filesystems.


delaylog,largefiles,nodatainlog,mincache=direct,convosync=direct

REdirecting the convosync and mincache is an speed enhancing procdure.

The are advanced features so be sure you have enabled vxenablef -a to ensure advanced features of vxfs are enabled.

these can be applied to a filesystem by using this command.

mount -o remount,delaylog,largefiles,nodatainlog,mincache=direct,convosync=direct


This provides maximum speed... for your DB... I also use largefiles b/c my DBAs require it... not necessary for you though

[Leif Halvarsson_2 · Accepted solution]

Hi,

I will try to give some ideas as I have the same problems as you. We are going to move a number of databases to a EVA array.

"But apparently, it's better to stripe all the Oracle data across 1 LUN rather than 2 separate ones."

I suppose you mean one or two Disk groups or RAID sets, 1 or 2 LUNs makes no difference if the LUNs is in the same RAID set. The general recommendation (for performance)is to use as many disks as possible in each RAID set (or disk group). For an EVA array, just one disk group.


"Anybody done any comparisons on the effect of RAID 5 vx."

It may be differences between RAID controllers but, as I understand, very important is the database read/write ratio. If this ratio is high (for example 80/20) you will get very little performance improvement with RAID 1+0.