Wednesday, July 23, 2008

Disk tuning [i]

 

Device level Disk delay:

 

  1. R/W Head delay or seek delay
  2. Data transmission delay
  3. Rotational delay

In 64 bit Oracle the parameter "db_cache_size" is only limited by the server.

So it's possible to run a "full-catched" database.

 

SQL> select SIZE_FOR_ESTIMATE,SIZE_FACTOR,BUFFERS_FOR_ESTIMATE,ESTD_PHYSICAL_READS from v$db_cache_advice;

SIZE_FOR_ESTIMATE SIZE_FACTOR BUFFERS_FOR_ESTIMATE ESTD_PHYSICAL_READS
----------------- ----------- -------------------- -------------------
              192       .0769                23670             4715108
              384       .1538                47340             2398212
              576       .2308                71010              858516
              768       .3077                94680              761897
              960       .3846               118350              697175
             1152       .4615               142020              636725
             1344       .5385               165690              600961
             1536       .6154               189360              588022
             1728       .6923               213030              586088
             1920       .7692               236700              585395
             2112       .8462               260370              585300

SIZE_FOR_ESTIMATE SIZE_FACTOR BUFFERS_FOR_ESTIMATE ESTD_PHYSICAL_READS
----------------- ----------- -------------------- -------------------
             2304       .9231               284040              585300
             2496           1               307710              585300 <- 100%
             2688      1.0769               331380              585300
             2880      1.1538               355050              585300
             3072      1.2308               378720              585300
             3264      1.3077               402390              585300
             3456      1.3846               426060              585300
             3648      1.4615               449730              585300
             3840      1.5385               473400              585300 <- but increasing the size, in this case, is not bringing much change

20 rows selected.

RAID and Oracle:

For databases that need a high volume of updates RAID 5 is not at all the solution.

Oracle suggests that ASM should be used with RAID 1+0 for best performance.

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