Re: Informix and EMC
Paul Watson wrote: > > Neil Truby wrote: > > > > IMHO the cache on the disk arrays makes it so fast that, for many > > applications with moderately-sized databases and I/O demands, it's not even > > worth the bother of trying to do anything special in configuration. > > > > I wouldn't mind betting that there'll be some dissent from this view though! > > I'd tend to agree. I once compared a fully optimised 'pure disk' > solution with > a non-optimised HDS RAID solution, the system was a small 100GB > warehouse. > The RAID had 64MB cache, and was 90% faster than the 'pure disk' > solution. > However, if you can then tune the RAID the performance can be amazing > when > compared to what you started with. We say disk write confirmation fall > from 25ms to 0.15ms One of the very best optimizations you can make is to vary the stripe block size to match the number of cylinders in each disk zone. All modern SCSI drives are zoned, ie the first N cylinders have k sectors each then next M cylinders have j sectors each etc., and taking advantage of the zoning so that a stripe read does not ever span a cylinder gap can make a big difference in performance. The main rub to this is that some drive manufacturers seem to feel that their zoning map is a trade secret. Seagate is the main culprit in this silliness. Art S. Kagel
Art S. Kagel wrote in message <38566527.500A772A@bloomberg.net>... >One of the very best optimizations you can make is to vary the stripe block >size to match the number of cylinders in each disk zone. All modern SCSI >drives are zoned, ie the first N cylinders have k sectors each then next >M cylinders have j sectors each etc., and taking advantage of the zoning so >that a stripe read does not ever span a cylinder gap can make a big >difference in performance. No, really, I'd take issue with this. Your analysis is correct, but for moderately stressed systems, on EMC (the subject of the original question) placement will not make a BIG difference. In my experience. Neil
Neil Truby wrote: > > Art S. Kagel wrote in message <38566527.500A772A@bloomberg.net>... > >One of the very best optimizations you can make is to vary the stripe block > >size to match the number of cylinders in each disk zone. All modern SCSI > >drives are zoned, ie the first N cylinders have k sectors each then next > >M cylinders have j sectors each etc., and taking advantage of the zoning so > >that a stripe read does not ever span a cylinder gap can make a big > >difference in performance. > > No, really, I'd take issue with this. Your analysis is correct, but for > moderately stressed systems, on EMC (the subject of the original question) > placement will not make a BIG difference. Actually the original question was "how to best configure an Informix instance ( 7.24 ) on HPUX 10.20 using EMC disk arrays". Since everyone was commenting on the EMC setup I thought I'd add my $0.02US. I agree with a large enough array, setup say as RAID10, and especially if you zone the stripes, placement on the disk, inside -vs- mid -vs- outside, will not make a significant difference and I do not worry about that anymore. Since using 20 and 30 drive pair RAID10 arrays across 4 pairs of controllers it's just not an issue. Art S. Kagel