Re: Raw I/O vs files (was Re: Raw partitions / cooked files)

->From: peno@kps.se (Pekka Nousiainen /DP) ->Subject: Re: Raw I/O vs files (was Re: Raw partitions / cooked files) ->Date: 28 Jul 93 21:03:03 GMT ->Reply-To: peno@kps.se (Pekka Nousiainen /DP) ->Organization: Kuwait Petroleum, Stockholm, Sweden -> ->In article <2506@coyote.UUCP> gainer@slowmo.almaden.ibm.com (P. Gainer) writes: ->>How many DBAs are running Oracle/Informix/etc etc using raw I/O? Any? -> ->I suppose small db's use files and large db's usually use raw devices. -> ->I don't have figures on performance. But it is clear that a properly ->implemented db kernel can use raw devices better because it *knows* the data. ->(Oracle V5 was very poorly implemented in this sense). For small db's ->I don't think there is much difference in performance between file vs. raw. ->For large db's (with large buffer caches) I think there is some difference. ->Of course it depends on many things. -> ->I have always (last 5 years) used raw devices. The reason is not performance ->but convenience, and it makes sense only for large databases. In current ->setup we have 14 disks (1.7 GB seagates) dedicated to the db. I split each ->disk in 4 pieces and use the pieces (mirrored) as db files. It's simpler ->than maintaining many mirrored filesystems and db files in those file systems. ->I also feel safer with raw devices: a careless rm or a file system error ->can't delete the db files. -> ->- peno@kps.se I think that Pekka has summarized things well, but not gone quite far enough. I would like to make two additions to Pekka's statement: 1. Small to intermediate sized DBs can profitably use the file system while ^^^^^^^^^^^^^^^^^^ large DBs probably need raw devices. 2. Designers/DBAs of small to intermediate sized DBs should consider using Standard Engine, rather than OnLine. Tuning and maintenance of OnLine engines is clearly a large task. Tuning and maintenance of Standard Engines is negligible. It seems foolish to take on the added task load unless there will be a reasonable return on the labor invested. Obviously people's ideas of what constitutes small, intermediate, and large databases will vary. High transaction volume on a middle-sized DB will kick it into the large category. By the same token, a HUGE database that is queried moderately and updated rarely (maybe a historical research DB???) can be treated more like a middle-sized DB. Regards, Alan +---------------------------+--------------------------------------------+ | R. Alan Popiel | Internet: alan@den.mmc.com | | Martin Marietta, Tech Ops | Voice: 303-977-9998 | | P.O. Box 179, M/S 5422 | My opinions may not reflect Martin policy. | | Denver, CO 80201-0179 USA | In fact, we often disagree. | +---------------------------+--------------------------------------------+