Exadata: Smart Flash Logging

"Exadata Smart Flash Logging” uses flash storage in the storage server to help database  to avoid latency writing to online redo logs. This small amount of flash memory temporary record the online redologs on flashlog created on flashdisks 

“ cellsrv " manages I/O processing on exadata servers. Oracle database consists of on line redo logs. when ever a transaction is committed, log writer writes the data from redo buffer cache to online redo logs. online redo logs are stored on storage severs. Here database interacts with Exadata server process “ cellsrv  “ to write the data to online redologs. simultaneously when request is completed it notifies the database.  

On the storage server, we have 4 FLASHPCI’S. Each consists of 4 flashdisks. We can check flashdisks on any Exadata storage using following command

cellcli> list clerks where disktype=flashdisk

when ever we got list of flashdisk on the storage server, we can go ahead and create flash log on single flashdisk available on the storage server

cellcli> create flash log celldisk=‘<flashdisk>’, size <>

following command displays, the flashlog available on the server

cellcli> list flashlog

cellcli> list flashlog detail 

or we can create on all storage cells as follows
In order to create the flashlog, we need to drop the existing flashcache and create the flash log and recreate the flashcache 
cellcli> create flashlog all
cellcli> create flashcache all

cellcli> list flashlog detail 

References:

http://www.oracle.com/technetwork/pt/articles/database-performance/exadata-smart-flash-logging-2132507-ptb.html

--Nikhil Tatineni--
--Exadata--