Workload and Resource Management
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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