RE: Cook device vs. Raw device
I haven't been following this thread to closely, so pardon me if I am repeating someone else's observation; but I always thought the most important difference between raw I/O vs. cooked I/O was data integrity following a crash. Cooked I/O might report a change as committed, while in reality the data has only been committed to the disk cache/buffer. With raw I/O, the data is committed to disk by the engine not the OS. Walt > -----Original Message----- > From: William Rice [SMTP:ricew@operamail.com] > Sent: Wednesday, September 15, 1999 3:02 PM > To: William Rice > Cc: informix-list > Subject: RE: Cook device vs Raw device > > This is a thread that has always interested me. I have been reading this > group for awhile, and was concerned when I came to my current place of > employment > and discovered they were using filesystems to hold data. When we > got the oppurtunity to do some limited testing on raw vs cooked we > could only find at most a 1.5% difference between informix's performance > to raw disk vs. cooked. > We watched the following things: > iostat, > vmstat > wall time > > We were running AIX 4.3.2 on a 520 > Informix 7.31UC2 > > Only 2 disk drives, one of which was dedicated to informix data. > Under 2 Gigabytes of data in the whole database > > These processes were simple queries(no more than three tables joined) > and the loading of data into tables. > > The longest running process was somewhere around 15 minutes. > The processes tested caused the system to be heavily io bound for some > and CPU for others. > > From reading the newsgroup I got the impression that I could count on at > least > a 10% difference between cooked and raw, yet the tests I ran did not turn > out > that way. > > The data involved was literally identical. I was curious what factors > might > be causing the performance not to increase. > > Will > > ------------------------------------------------------------ > This e-mail has been sent to you courtesy of OperaMail, a > free web-based service from Opera Software, makers of > the award-winning Web Browser - http://www.operasoftware.com > ------------------------------------------------------------