Re: Compaq tell me I cannot use hardware raid and raw disks with informix

From memory the idea is to make the slice a multiple of the chunk size, and to use an offset that is also equal to the chunk size. This is referred to by informix engineers as 'alignment' and has been shown to provide as much as a 20% performance increase over non-aligned systems. One thing to watch in using Raid 5 as a cheaper alternative to full disk mirroring as David suggests is the huge cost for performing writes (you write to every spindle in the array afterall). In the same testing environment mentioned above, they found that the use of a write cache gave a 90% performance increase. You just need to decide how important the data is to you, just don't go using RAID 5 for things that have very high activity such as tempdbspace, logspace etc. If Compaq have recommended that hardware raid and raw disks cannot be used with Informix they are sorely mistaken, you should be careful in using RAID 5 for any database application, its not specific to vendors. regards Ben. David Kosenko wrote: > "Dennis JR Harding" <dennish@wpr.co.za> offerred: > :Further, it is advisable to use the Informix mirroring method above any > :other logical method. Online 7 will optimize to use mirror disks with the > :primary disk in executing SELECTS, so doing also increasing performance. > > Be careful here. The optimization is not all that sophisticated. All it does > is break the chunk "logically" in half, so read requests from the first half of > the chunk are satisfied from the primary; read requests from the second half are > satisfied from the mirror. If the chunk is not fully used, or worse yet, less > than half used, there would be little to no appreciable performance impact. > > Also, one has to bear in mind that the cost of raid 5 is typically much lower > than mirroring, as you don't require 100% disk overhead as with mirroring. Cost > of hardware is still an issue for a lot of folks. > > While it is certainly easier to use straight disks rather than a raid config (as > it makes it very easy to map dbspace to physical disk that way), Informix > engineers have done some testing in the past to determine how online and raid > work together. I don't have any copies of the results handy, but I do recall > that it was reported that the two were not incompatible. I believe the > recommendation was to make the chunk size == slice size or somesuch. > > Dave > ********** > "Everybody plays the fool, sometimes."