Re: Anybody use HP AutoRAID with an Oracle DW?

On 2 Jul 1998 23:14:46 GMT, weghorst_at_nilenet.com (Mark Weghorst) wrote:

>MCR (mrush_at_hertz.bogus.com) wrote:

Like Mark, I have only OLTP experience(Oracle7) with the 12H and all of it good. The read/write cache does delay writes, this is why there is a built in battery backup in each controller. However, when the system is not under a heavy write load it is probably an instantaneous write to disk.

Another great thing about the 12H is the ability to hot swap components. I have pulled out disks, power modules and fans without a problem. Not because they failed, but just to see if it worked as advertised.

While it is true that you cannot control which device gets your write(they all do), You can control what controller path the reads and writes take(X or Y). The AutoRAID manual suggest you do this. I was careful to spread my I/O across the two controllers to avoid any possibility of saturating a SCSI path. For example, I put my Redo on one and Archive Logs on the other and my tables on one and my indexes on the other. My UNIX box is configured with 2 FWD controllers going to the RAID box.

12H performance takes a nose dive when your write working set cannot be kept in 0+1. The documentation claims that the 12H reserves 10% of the space on the array for this purpose. This may not always be enough. As I understand it, you would only see a drop in performance at 50% capcity if your write working set was 50%. If your write working set does not exceed 10% you could use all available sapce(if it truely is reserving 10% for the write working set) and not see a drop in performance. If you know that your write working set is going to be greater than available 0+1 you may want to consider putting TEMP on some other device outside of the RAID box, or allocate LUNs in a such a way that you always have enough write working set.

If your DW application is mostly reads during business hours, your daytime performance should be great. The User's Manual and System Administrators Manuals for the AutoRAID are very good and are where I learned most of what I know about AutoRAID. Oracle has some notes available concerning using RAID with Oracle. Look at Solution# 2059721.6 "A Brief Overview of RAID and Oracle". Keep in mind that the RAID this article is talking about is not AutoRAID. The cons they talk about apply only when your write working set cannot remain in 0+1. The article basically warns against putting TEMP, Online Redos, and Archived Redos on RAID5. I put TEMP on an internal system disk, but left Redos on the RAID box and I have had no problems. If I had had the time I would have run some bench marks on TEMP, but I did not.

Carefully plan how much disk space you will need. Read the part in the manual about assigning disk space to LUNS and the maximum number of LUNS you can have . Allocating all LUNS can improve performance but make adding disk space more complicated. Also read carefully the section in the User's Manual title "Write Working Set", "Increasing the Amount of RAID 0/1 Space Availalbe", and "Won't Deleting Files Increase RAID 0/1 Space?" in chapter 4.

In addition, there is some theoretical benefit to having all disk slots populated - more internal data paths or something. In light of these considerations and the relative low cost, the second box I bought was fully populated with 9.1GB drives.

Ken

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Ken Walters
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