Low Buffer cache Hit Ratio's & I/O bottlenecks

[keith persons]

A word of caution, the mincache and convosync mount options should be used ONLY for the database mount point ONLY. Using these options on other file systems can heavily degrade throughput.

[Tim D Fulford]

On the cooked V raw I have an opionion...

I'm an Informix guy and saw the comments about Informix using raw LVM and Oracle using cooked. The reasoning is really quite simple.

1 - Efficient use of memory - Dbase buffers keep most frequently/recent used pages there - HP-UX buffer cache is used to keep most recent pages there. If you have an OLTP DBase (NOT OLAP, or DSS as these tend to flush the buffers anyway), then using cooked filesystems means that the pages are in memory twice, one in the DBase buffers & one in buffer cache, very inefficient.
2 - There is a possiblity that the DBase could do a write & crash before the buffer cache has flused to disk
Given the above you would pick raw....

On the other hand....
1 - It is easier to defragment a cooked filesystem & therefore improve performance this way.
2 - Memory is cheap & plentiful.
3 - The performance of cooked filesystems can be better than raw (so I'm told).
4 - JFS should not allow any data loss

From the above you can see there are arguments either way and it tends to be that people take up what their vendors say.

On the % cache ratio, if you copied the raw LV's to raw LV's it should not pass through the buffercache at all....

That way my 0.02??? worth

Tim