Re: Informix 7.x and RAID 5

Jim, >Though I agree with a lot of what you say here Mike, I think you also have to >consider that this is for data warehouse environment. To mirror this database >is going to require 60-200+Gb of disk. I doubt that the data warehouse truely >requires the same level of availability of the oltp type systems you discuss >and the cost of this amount of disk is substantial. If you look at the price difference you rarely get that much more for your money. In fact, I have seen cases where RAID actually cost the same amount as mirroring because of the cost of the RAID subsystem. These things are not as cheap as everyone thinks. With disk prices where they are today 200 Gb of disk would cost around $50,000 to $80,000. This seems pretty inexpensive to me when you consider that a 20 Gb Clairion can cost upwards of $50,000 itself. Benchmarks have shown that DG's Clairion system is about as fast as Informix using round robin fragmentation. Informix with expression fragmentation allows the engine to eliminate fragments when it is searching for a particular set of values. This can be substantially faster than round robin or RAID. > >In addition another Informix employee recently pointed out that, for databases >of this size, if each RAID 5 sub-system is treated by Informix as a single >drive you can get the best of both worlds. Fragmentation and chunk partioning >across several RAID sub-systems to achieve the parallel access through DSA with >the RAID providing a cost efficient level of availability and access speed. There is a limit on chunk sizes, offset+size <= 2 Gb. This is partially because of the fact that lseek uses a long integer for the number of bytes to seek. With this limitation you would have to have many 2 Gb RAID subsystems for each one to be a chunk. Another benifit of smaller dbspaces is restore times. If you have huge dbspaces and the disks it resides on crashes then you have a much larger potential for user interruption. With smaller devices the restore can happen faster and the dbspace can be back online faster. Mike Mike Flannery Professional Services Engineer Informix Software Inc. Email : flannery@informix.com Phone: (913) 599-8407 Fax : (913) 599-8484