UNIX for Dummies Questions & Answers

Hi all,

My main function is as a DBA. Another person manages the server and the SAN.

I just want to know if I should be worried about high disk I/O or is it irrelevant as the I/O "load balancing" will be "taken care" of by the SAN?

For example, I have hdisk1-5 and I can see that there are high disk activity for hdisk1-3 but minimal on hdisk4-5, should I be concern and move database files from hdisk1-3 to hdisk4-5 and spread them around?

FYI, I can account for when hdisk1-3 are busy which is during the data load but while this is expected, I am thinking maybe it will "help the SAN" if I move out some of the database files to the filesystem where hdisk4-4 are assigned to.

Any input will be much appreciated. Thanks in advance.

Moderator's Comments:

Moved to "Dummies" forum.

Normally a logical volume (lun) is based on all of the disks in a given SAN device. You do not tell the SAN where to store a lun. Period.

The SAN software can be confiured for different types of RAID settings and SAN software does all sorts of tuning and caching. If what you saw is WAY out of line, ask your disk guy to monitor what is going on. He/she can make adjustments.

The "disk" stuff you see df -h or iostat in the OS is the logical presentation of a filesystem on the OS, never a single physical disk. Don't conflate logical volumes and physical disks, which is what you seem to be doing.

are you actually seeing performance problems? the old rule is don't fix something if it's not broke. Don't try to "help the SAN". What your really saying is how can I minimize the disk I/O for a given server which is a good thing for a database server.

yes - you can create more file systems and spread tablespaces around. This can help performance even if the data is on the same LUNs. You can get benefits from OS file system caching and parallel I/O. check your bufferpool hit ratios. make sure your logs and tablespace data are in different file systems at minimum.