Exadata Smart Flash Cache

Exadata Smart Flash Cache: Is a write-through cache, disk cache on exadata storage server. It caches data for all instances that access the storage cell.

Different types of I/O from database:

Caching: 
Control file reads and writes are cached
File header reads and writes are cached
Data Blocks and Index blocks are cached

Skip Caching:
I/Os mirror copies, backups, data pump, tablespace formating, resistant to tables scan are skipped.

For a full rack, you cannot use more than 4.3TB (about 80% total flash available for smart flash) for "KEEP".  In some situations, an object with "KEEP" is left flash, it could be that the object is not accessed in 48 hours, block not accesses in last 24 hrs or object dropped or truncated.


To create Exadata Smart Flash Cache:
CellCLI> list celldisk attributes name, disktype, size where name like 'FD.*'
FD_00_cell FlashDisk 496M
FD_01_cell FlashDisk 496M
FD_02_cell FlashDisk 496M
FD_03_cell FlashDisk 496M

CellCLI> create flashcache all size=1000m;
Flash cache cell_FLASHCACHE successfully created

CellCLI> list flashcache detail;
name: cell_FLASHCACHE
cellDisk: FD_01_cell,FD_03_cell,FD_02_cell,FD_00_cell
creationTime: 2013-01-28T16:38:18-08:00
degradedCelldisks:
effectiveCacheSize: 960M
id: 2f225eb8-d9e3-41a6-a7d8-691dd04809b5
size: 960M
status: normal

CellCLI> list griddisk
data2_CD_disk01_cell active
data2_CD_disk02_cell active
data2_CD_disk03_cell active
data2_CD_disk04_cell active
data2_CD_disk05_cell active
data2_CD_disk06_cell active
reco_CD_disk07_cell active
reco_CD_disk08_cell active
reco_CD_disk09_cell active
reco_CD_disk10_cell active

CellCLI> create griddisk all flashdisk prefix=flash;
GridDisk flash_FD_00_cell successfully created
GridDisk flash_FD_01_cell successfully created
GridDisk flash_FD_02_cell successfully created
GridDisk flash_FD_03_cell successfully created

CellCLI> list griddisk
data2_CD_disk01_cell active
data2_CD_disk02_cell active
data2_CD_disk03_cell active
data2_CD_disk04_cell active
data2_CD_disk05_cell active
data2_CD_disk06_cell active
flash_FD_00_cell active
flash_FD_01_cell active
flash_FD_02_cell active
flash_FD_03_cell active
reco_CD_disk07_cell active
reco_CD_disk08_cell active
reco_CD_disk09_cell active
reco_CD_disk10_cell active

Objects will be cached in the Exadata Smart Flash Cache based on the automatic caching policy. But you can control the policy of a database objects using these three attributes: NONE (never cache), DEFAULT: automatic caching mechanism, KEEP: more aggressive caching.

SQL> alter table anguyen.mycustomers storage (cell_flash_cache keep);

Table altered.