RE: Oracle configuration on SAN

A 14-drive RAID-5 set is very large. It's certainly functional, but the two problems you'll run into is problems with spindle contention and rebuild times. With a 14-drive set, your drive is getting cut into 14 columns, so that there's 14 different disk regions per drive it might have to seek to in order to service any given I/O. That can negatively impact performance on random writes. Have you tested failing out a drive under load? On a 14-drive set the rebuild time is going to be pretty horrendous, and your performance will likely be impacted unless your cache hit numbers are really great.

The other problem is that by carving luns globally out of a single RAID-5 set, differing i/o patterns on the luns can create hot spots much more easily, since your small (comparatively, anyway) redo log volume (for exmaple) ends up on only four columns of the disks, and other volumes on other columns on those disks can be hurt by the constant writing.

While I'm not necessarily as anti-RAID 5 as some (though I give all due respect and worship to our mighty BAARF leaders), you need to keep a very close eye on your array in this configuration. If you have a normal OLTP workload (whatever "normal" is), play with your cache allocations - the read v. write cache, and if you can do per-lun tweaking, weight the redo and archive log lun(s) very heavily towards write cache.

If you're set on RAID-5, I would recommend taking two of the disks and making them a mirrored pair for redo and archive logs. Since the writes tend to be reasonably contiguous, the fact you're hitting just one set of spindles shouldn't hurt quite as bad, and cache should take the edge off a bit.

This all being said, my knowledge of that particular HP array is limited at best, so I can't offer vendor-specific recommendations/thoughts that might invalidate some of these concerns. Good luck.

Thanks,
Matt

--
Matthew Zito
GridApp Systems
Email: mzito_at_gridapp.com
Cell: 646-220-3551
Phone: 212-358-8211 x 359
http://www.gridapp.com



> -----Original Message-----

> From: ml-errors_at_fatcity.com [mailto:ml-errors_at_fatcity.com] On 

> Behalf Of Sherrie.Kubis_at_swfwmd.state.fl.us

> Sent: Monday, July 21, 2003 1:49 PM

> To: Multiple recipients of list ORACLE-L

> Subject: Oracle configuration on SAN

> 

> 

> Dear Listers,

> 

> I'm looking for advice on configuring Oracle under a SAN.  We 

> just got a new box, an HP UX, with an HP CASA that's 

> connected to an HP MSA1000 with fourteen 72gb drives 

> configured as RAID-5 with Advanced Data Guard, and two global 

> hot spares on that drive shelf.  All of this is connected to 

> the HP through two-gb fiber channel host bus adapters.  So 

> far, four 75 gb LUNs have been created so that the primary 

> path to the CASA is shared between the two HBAs, providing 

> some load balance between the LUNs -- LUN1 & LUN3 on HBA, 

> LUN2 & LUN4 on the other.

> 

> Given, this, are there any recommendations for Oracle's 

> configuration? Control file, redo placement? Maybe indexes 

> and data placement don't mean as much any more, but files for 

> recovery should be treated in a different manner.

> 

> Any insights or experience would be helpful.  Most of the 

> information that I've found is marketing, and a description 

> of what SANs are.  I'm looking for recommendations for Oracle 

> configuration.  Everything I find on OTN sends me to the 

> vendor, but the vendor doesn't have anything specific to Oracle.

> 

> 

> 

> 

> ---------------

> Sherrie Kubis

> Southwest Florida Water Management District

> 2379 Broad Street

> Brooksville FL 34604-6899

> 

> Phone:  (352) 796-7211, Ext. 4033

> Fax:     (352) 754-6776

> Email:  Mailto:Sherrie.Kubis_at_swfwmd.state.fl.us

> http://WaterMatters.org

> 

> 

> 

> 

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