Re: Informix disk mirroring

John Coyle wrote: > > Hi everybody! > > I'm investigating the efficiencies of disk mirroring for our Informix > 7.23.UC3 engine on an HPUX 10.2 box. I am currently mirroring the root > dbspace as well as the physical and logical logs. We are thinking of > mirroring an entire 12Gb database. What are the efficiencies of Informix > mirroring over other forms of hardware mirroring? Does Informix support > mirroring to separate disks on the SAME SCSI channel or should I use > SEPARATE SCSI channels? Informix published a white paper a few years ago which is not online any longer in which they compared, on DG Aviion CPUs with DG Clariion RAID subsystems, RAID5 vs mirror and stripe and hardware mirror -vs- OS level software mirror -vs- Informix mirror for Informix databases. The results were revealing (these are from memory, I have to dig up the report, but they are about right). Hardware mirroring (at least on the Clarion subsystems) was the fastest by about 10%, OS software mirroring (again with DG/UX mirror software) was slower that Informix software mirroring by a few percentage points. (BTW in tests between RAID5 -vs- Informix mirror, mirroring was >25% faster.) If hardware mirroring is available use it unless the convenience of having the Informix tools available to manage it outweighs the 10% performance gain (I feel this way myself). If only software mirrors are available definitely use Informix mirroring. Informix mirroring, like most software and many hardware mirrors, will let you mirror any two devices that are the same size (specifically as long as the mirror is at least as large as the primary) so you CAN put both sides of the mirror on the same controller. I would STRONGLY recommend that you not only use different controllers but separate power supplies (ie separate cabinets) as well to remove the possibility that one component can take out both sides of your mirror. Art S. Kagel