Re: Informix and RAID?

In article <91a7cc$a151c.3a5@news.leg.wa.gov>, test@test.com (Test IT) wrote: > The folks from Informix told me that running Informix on a box in a > RAID configuration is not the best idea. They say that performance > drops. Is anyone running Informix 7.11 or > on a RAID box? We're > talking less than 100 tps and less than 20GB of data. If you > converted from not RAID to RAID, did you see a big performance drop? > > If people aren't using RAID how do they deal with fault tolerance? > Morroring? I'm about ready to go production and I'm at the point > where I need to buy a production server. I don't want to screw up > Informix, but I sure like the warm and fuzzy feeling of RAID. > > Thanks for any comments/suggestions > > Jason Fry > Washington State Legislative Service Center > fry_ja@leg.wa.gov Hi, All this noise about not using RAID for Informix started because of some tests that were carried out by Informix on CERTAIN types of RAID. In fact as far as I know one it was actually only one particular RAID box. The box was tested inside and out, and the various results ranged from poor to average, and never on a par with JBOD. The resources necessary to carry out all this were extreme, and I can't really blame anyone for not being able to repeat it with a fast RAID system, or even having the time and opportunity to do it all over again - availability of h/w, resources, time etc. The results have been informally distributed within the trade but rarely for public viewing. Results back from the field have re-inforced the findings, and, by the way, the same topic keeps appearing in all RDBMS newsgroups, that is: anything based around RAID5 or independent RAID or Dynamic RAID has the *capability* to shoot performance in the foot. Comments in the Sybase newsgroup, for example, have included "RAID5, don't use it!". (however note that people with low write load and low I/O loads never see a problem wih RAID5 - so it is OK for them) The result has been a general attitude by Informix to say, keep away from RAID. It has been the easy path, and keeps them out of particular RAID product-specific performance arguments. Again, I can't blame them, they are a massive s/w company with competitive product, and hardware functionality is not their game or an area to get involved with. However, let us look at the things that affect RAID performance in the Informix environment. 1) Alignment of volume / stripe / page size / chunk - get it wrong and the RAID will be doing multiple operations for most transactions. This needs to be tuned for each RAID volume. 2) write performance - Even some RAID systems which claim to write cache have pretty poor write performance. This needs to be actually measured under load for each different system under consideration. 3) Fragmentation - Informix likes to break up the volumes and carry out parallel operations on the available physical volumes. This is undone by RAID, where several volumes could in fact share the same physical disks in a RAID. This last issue is raised by Informix as a big problem. Fragmentation is a key Informix mechanism to increase paralellism and thereby increase throughput. If the parallel operations ultimately return to the same spindles then the bottleneck comes back. However, this is a performance issue. Use a fast enough RAID system and this problem becomes a non-issue, or trivial. It doesn't go away, it just becomes less unimportant. The issues with RAID don't stop here. Different RAID systems have very different capabilities when it comes to handling disk and data errors. Again, only last week one RAID vendor posted a query in one of the database newsgroups asking if the RDBMS had its own disk bad block list. Why? I guess they don't trust their data, so why should you? p.s. my name is changed in my email address because I don't like the way that Alta-Vista and the others are keeping a history on us all. Contact me directly if you want to know more about RAID and Informix. It can be safe and high performing. Glenn