Creating LUNS

[Charles Fear]

Currently I have 6 9.1GB drives in one 12-H AutoRAID Array. We are planning to replace these drives and fully populate the RAID array with 36.4 GB drives. They should be here in approx. 3 more days. The question I have is regarding the size and quantity of LUNS. Understanding the max is 8 LUNS and that performance will be increased by the greater number of LUNS. Since the 12-H will be instantly maxed out should I jump to the 8 LUN limit or tone that down to 6.

The intent is to create 2 VGs and 8 logical volumes stratigically assigned to the 2 VGs. The purpose for 2 VGs is to designate a separate primary and alternate controller for the oracle data files and the oracle indexes.

Maybe I'm way off base and if so please be brutal.

Additionally, this storage space is just a temp solution as we complete our project plan to bring in an EMC 3930 with 2 TB usable. At that time this data will all migrate so I don't se much change from this configuration till then, however, with programmers and developers you can never tell.


Thanks

Charles

[A. Clay Stephenson]

Hi Charles,

I've actually got Oracle running on some on my boxes using 12H's. Here are my rules (and I've measured) for getting the most out of Oracle on AutoRAID's. If you don't already have OnlineJFS, buy it. No HP-UX box should be without it for any number of reasons.

1) You really only need 2 LUN's per ORACLE instance. I think the myth of multiple LUN's arose out of Glance/Measureware APPEARING to indicate overloaded devices. The Measureware tools are not very good when looking at arrays; they can't be. All they see is one device. Dividing your array into more than 2 only makes things APPEAR better but performance remain the same. It's better to save the LUN's for later use. Compute the total amount of space your database will require including archive logs and redo logs.
Create 2 equally sized LUN's that together equal your required Oracle space.
2) Create just two logical volumes but striped across both LUN's in 64K chunks. (Vxfs likes to write at that size). You want LUN0's primary path through controller X (alternate Y) and LUN1 primary path through controller Y (alternate X). This will fully utilize both external SCSI busses and increase your throughput by about 50%.
3) lvol1 will be used to store both the data and the indices. (Now don't have a duck - with the AutoRAID you have no control over the physial layout anyway).
4) lvol2 will be used to store the archive and redo logs.
5) Mount lvol1 with vxfs options convosync=direct,mincache=direct,nodatainlog
(This will bypass the unix buffers and give
you essentially all the benefits of raw i/o while still using cooked files.)
6) Mount lvol2 with the conventional options. I find the archive and redo logs do better with the unix buffers.
7) Because you are bypassing so much of the UNIX buffers, you can decrease your filesystem buffers and thus allocate more buffering in the SGA where it belongs. My favorite method for database servers is to turn off dynamic buffer caches by setting bufpages to a value of about 300 MB and that is generous).
8) Allocate no more that about 60% (and less is better) of your total 12H capacity as LUNS.
This will keep all your data in RAID 1/0 and again performance will increase.

If you follow these steps, I think you will be quite surprised at how well the old 12H's perform.

The best advice I can give you is: don't take my word for this - measure.

My 2 cents worth, Clay

[David Allen]

Hi Charles,

I agree with what Clay has written, in fact there are a few points that I wasn't aware of and will certainly look into if I need to setup a 12H again.

The only thing I really have to add, is that it always pays to keep some disk space unallocated and have a couple spare LUNs available. Because, as sure as the sun sets in the West, the programmers and developers will suddenly decide they need more disk space.

Cheers, Dave

[Curt Thompson]

Hello Charles,

I agree with the previous posts regarding keeping some space unallocated, but for a different raeson: performance. Unallocated space helps the 12H maintain data in RAID 0/1
instead of RAID 5.

Also, don't forget about your fans. No, not the ones that admire you, but the ones located above the disk drives. 36GB drives use the 10K RPM disks and require the higher output fans.
High output fans have a raised, clear bubble over the fan logo.

Good Luck,
Curt