Re: Machine Configuration

Enio Roncarati wrote: > > Hi everybody. > > We have a version 7.20 of Informix OnLine Dynamic Server on a DEC 2100 with > 3 CPUs, 1 GB of RAM and 60 GB of Storage Array. > > Everything is OK, but we want to find the best configuration for the disk > array. We have 2 disks array of 30 GB each, on 2 different controlers, each > one with 4 channels. Each array has 6 HZ40 from DIGITAL, that support bolth > raid level 3 and 5. > Probally, we will have much more "READS" than "WRITES". We know that there > is a big difference from raid level 3 and 5 when reading information from > a database, and in bolth cases the chunk size parameter is very important. We have an OLTP application running on an HP T500 with 6 cpu's, 2 gig ram and are using MTI raid. We have 2 separate raid devices on separate controllers and we also have 2 16-gig and 2 20-gig devices on separate controllers as well. Our application has a lot o reads similar to yours. We initially set up our Informix instance out on the raid devices and turned on Raid level 5. Our database was not maintained for quite some time and we had a very bad problem with our tables being extremely fragmented...lots of extents... Anyway, this does not work well with Raid 5...mainly because you are performing striping with parity across the Lun..Since all of the tables were extremely fragmented we took tremendous hits during the writes. Another problem was read the Controller Read Ahead setting on the Raid device was turned on. The stripe depth was set to 8k pages. Well....the page size on the server was 2k pages so it was reading 8k every time instead of just 2k pages so you can see we took bit hits even with the reads and fragmentation combined. We've moved a lot of our heavy insert tables off of Raid and striped them out on some other 16 gig drives and have left our read only stuff out on Raid. After talking with the Raid vendor..here's what we may try if we go back to Raid. Use Raid 0+1 for most of the heavily hit tables, temp, root, logs, etc etc.. Then use Raid 5 for the rest. Raid 0+1 is mirroring and striping as well so you'll have good recovery capability if a disk goes out. You may also want to keep another raid disk around in case one fails. I hope this is not too confusing, there are a lot of things to be concerned with when using raid devices and I learned the hard way and it took a lot of hours to get the system running correctly. Get with your Raid vendor and get a good understanding of the capabilities of your storage array and make sure your database is sized correctly. I hope that some of these things may help you out in planning. Tks Ed edbid @ cobe.com