Re: Q: Mirroring - what is the better way
In article <6915mt$qdg@cssun.mathcs.emory.edu>, Robert Wines <Robert_Wines@emsinfo.com> writes > > >Pablo Sanchez wrote: >> >> On Nov 17, 7:35am, Peter Tashkoff wrote: >> > Subject: Re: Q: Mirroring - what is the better way >> > >> > The writes in Informix are performed asynchously in parallel. > >> What makes you think that the device driver isn't doing the >> same? The SCSI bus can handle multiple requests and have >> many requests outstanding: command tag queuing. > >> I find it extremely hard to believe that Informix (or any >> other vendor s/w) could match the h/w vendor's *own* >> engineers. Furthermore you add an additional layer of >> software at the *user* level so you end up with less >> performance. But hey, if that's okay with you, go for it. > >> I'm consistently amazed how many people swallow the "Informix >> Line" with no question: >> >> o what? support needs to dial in to fix my db? ahm, >> okay, I'll buy support. >> o what? informix knows the hardware better than >> HP/Sun/SGI's engineer's? oh, okay... > >On this last actually they often do (rumor has it that the HP IO system >is much better thanks to Informix engineers). > >Rumor aside, Hardware mirroring tends to be fastest on raw read/write >tests and most hardware mirror systems include the same optimizations >that Informix mirroring does. OS/software mirroring tends to be >slightly slower than Informix mirroring on all of the benchmarks that I >have seen but not enough to affect a decision. There are several OS >mirror systems that DO NOT include the read/write optimizations that >Informix uses and update both disks in lockstep rather than >asynchronously, eliminating the possibility of reading from one side >while writing to the other. Most can split reads, but not all (Ultrix >could not). However, only Informix mirroring can be taken advantage of >by the PDQPRIORITY and Informix optimizer. If Informix knows that there >is a mirror extra threads will be launched and more parallelism is used. > >Art S. Kagel > >I have done some testing on a database with and without mirroring. The >tests were performed on the following system: > >DEC Alpha >The development machine is an AlphaServer 2000 4/233 which had the >following: >(2) Alpha 233 MHz CPUs >128MB Memory >(1) 2GB root disk >(1) 4GB home/tmp disk >72GB of RAID 5 disks >(1) DLT tape drive (20GB capacity at least) >(1) Ethernet Controller >(1) FDDI Controller > >Database consisted of >80 tables >6 GB is the size of the database > >The test consisted of running the most frequently used stored procedures >that our application runs. We used scripts running the stored procedures. > We ran the stored procedures individually and then we added users in >increments of 20. We used a warm-up period so the SPs were cached. The >results were roughly the same until we got to the 40 user mark at that point >the database with mirroring performed 20% better than the same database >without mirroring. The continued until the mirrored database was running >twice as fast at 80 users as the unmirrored ran at 80 users. I was very >suprised to say the least. > >Robert > >robert_wines@emsinfo.com > One for the FAQ.. PS Demon's news server was down so I'm a day behind. PPS Here's Robert Wine's Article [say you going to dejanews]. -- David Williams Maintainer of the Informix FAQ Primary site (Beta Version) http://www.smooth1.demon.co.uk Official site http://www.iiug.org/techinfo/faq/faq_top.html I see you standin', Standin' on your own, It's such a lonely place for you, For you to be If you need a shoulder, Or if you need a friend, I'll be here standing, Until the bitter end... So don't chastise me Or think I, I mean you harm... All I ever wanted Was for you To know that I care