Re: Disk Layout

Steve Romankiw wrote: > > I have been unable to find information reguarding the pros & cons of > RAID and ODS. > > We are running Sun Solaris 2.5.1 with VxVM and ODS 7.23 UC1. We > planning for some expansive growth in our database(s). In our Sparc > Some of the questions I have are: > > Q: Should I simply create two partitions per drive? This creates two > 2gb partitions which the max chunk size for ODS. > > Q: Should I employ RAID 0+1? Get the benefits of striping and > mirroring? > > Q: Is your decision different based upon OLTP vs DSS? We have found the best performance from our DG Clariion RAID subsystems by preparing a large stripe set from a large number of drives each of which has been mirrored onto a drive on another Clariion subsystem with separate controller and power supply. We use from 15, 20 & 30 drive stripe sets of 4 or 9 GB drives. DG firmware can then divide the 260GB pseudo-physical drive into 130 2GB logical drives. We then create a symbolic link to each of the raw devices in a single directory and add these (or pieces of them for smaller DBs) as our Informix chunks. Because of the wide stripe, the firmware level mirror, and the controller level caching performance is beautiful. I stopped testing with 100 processes pumping 30MB per second, total, out to the same logical raw device and the last addition of 10 more processes gained 7% increased throughput from the 11% increase in processes so there was still a little more throughput to squeeze out (this was with 4GB drives the 9GB drives rotate 30% faster so...). Obviously, if you do not need 270GB of storage you can adjust the stripe size accordingly. The keys seem to be 1) Stripe mirrored pairs so that the striping software can just write to each stripe member and the mirror firmware can load balance the two mirrors. 2) Get intelligent RAID arrays with large caches which can be used effectively for elevator sorting of writes. We added cached controllers the the Clariions last year while still using RAID 5. Performance improved dramatically (I/O waits reduced 75%) but the mirrors blow RAID 5 away for pure performance and are MUCH more reliable and yes 40% more expensive. Hope this helps. Art S. Kagel