Simpler Navigation for Servers and Operating Systems
Completed: a much simpler Servers and Operating Systems section of the Community. We combined many of the older boards, so you won't have to click through so many levels to get at the information you need. Check the consolidated boards here as many sub-forums are now single boards.
Showing results for 
Search instead for 
Did you mean: 

kernel parms & RAW disk I/O

Thomas C. McGivern
Occasional Contributor

kernel parms & RAW disk I/O

I see DBC_MIN/MAX_PCT, BUFPAGES, NBUF control how unix manages caching for disk I/O. Under the heading "filesystem I/O".

My system is a database server, accessed over the network, so very little "filesystem" I/O takes place, but a boat load of RAW disk I/O.

Do these parameters affect RAW I/O?
Bill Hassell
Honored Contributor

Re: kernel parms & RAW disk I/O

Immediate reporting will affect raw I/O as it tells the disk to accept write requests and report that they are already completed. This is not recommended unless *all* the disks on the system are backed up with a battery so that pending writes from the disk's RAM will be completed.

You can also look at the scsictl man page to selectively enable immediate reporting on a disk by disk basis. This will require a technical reference manual for the disk(s).

Generally, raw I/O performance is 100% controlled by the application. Popular database programs offer a lot of choices to increase buffer sizes, keep indexes and hash tables in RAM, etc. Simple rule: maximize RAM usage by the database program (and think several gigabytes for CPU RAM).

Bill Hassell, sysadmin