EXADATA Flash Cache Compression only on X3 & X4 Machines

Exadata Flash Cache Compression was introduced in Exadata Storage Software version 11.2.3.3.0

·   Flash cache compression dynamically increases the logical capacity of the flash cache by transparently compressing user data as it is loaded into the flash cache.

·   This allows much more data to be kept in flash, and decreases the need to access data on disk drives.

·   The compression and decompression operations are completely transparent to the application and database, and have no performance overhead, even when running at rates of millions of I/Os per second.

·   Depending on the user data compress ability, Oracle Exadata Storage Server Software dynamically expands the flash cache size up to two times. Compression benefits vary based on the redundancy in the data. Tables and indexes that are uncompressed have the largest space reductions. Tables and indexes that are OLTP compressed have significant space reductions. Tables that use Hybrid Columnar Compression have minimal space reductions.

·         Oracle Advanced Compression Option is required to enable flash cache compression.

How to enable Flash Cache compression in Rolling method

1. Flush the dirty blocks from Flash Disks to the Grid Disks

CellCLI> ALTER FLASHCACHE all flush

To monitor the flush operation, open a new cell cellcli session and run command:

CellCLI> LIST CELLDISK attributes name, flushstatus, flusherror

While flush operation is working, the attribute flushstatus will report working

CellCLI> LIST CELLDISK attributes name, flushstatus, flusherror
         CD_00_celadm08              
         CD_01_celadm08              
         CD_02_celadm08              
         CD_03_celadm08              
         CD_04_celadm08              
         CD_05_celadm08              
         CD_06_celadm08              
         CD_07_celadm08              
         CD_08_celadm08              
         CD_09_celadm08              
         CD_10_celadm08              
         CD_11_celadm08              
         FD_00_celadm08    working   
         FD_01_celadm08    working   
         FD_02_celadm08    working   
         FD_03_celadm08    working   
         FD_04_celadm08    working   
         FD_05_celadm08    working   
         FD_06_celadm08    working   
         FD_07_celadm08    working   
         FD_08_celadm08    working   
         FD_09_celadm08    working     

To validate that flush operation was successful use any of following methods, opening a new cellcli session

Attribute flushstatus reports complete

CellCLI> LIST CELLDISK attributes name, flushstatus, flusherror
         CD_00_celadm08              
         CD_01_celadm08              
         CD_02_celadm08              
         CD_03_celadm08              
         CD_04_celadm08              
         CD_05_celadm08              
         CD_06_celadm08              
         CD_07_celadm08              
         CD_08_celadm08              
         CD_09_celadm08              
         CD_10_celadm08              
         CD_11_celadm08              
         FD_00_celadm08    complete  
         FD_01_celadm08    complete  
         FD_02_celadm08    complete  
         FD_03_celadm08    complete  
         FD_04_celadm08    complete  
         FD_05_celadm08    complete  
         FD_06_celadm08    complete  
         FD_07_celadm08    complete  
         FD_08_celadm08    complete  
         FD_09_celadm08    complete   

     

Verify cachedby attribute is null.  If a FlashDisk is reported, flush is still in progress

CellCLI> LIST GRIDDISK attributes name,cachedby

CellCLI> list griddisk attributes name,cachedby
         DATA_DMORL_CD_00_celadm08
         DATA_DMORL_CD_01_celadm08
         DATA_DMORL_CD_02_celadm08
         DATA_DMORL_CD_03_celadm08
         DATA_DMORL_CD_04_celadm08
         DATA_DMORL_CD_05_celadm08
         DATA_DMORL_CD_06_celadm08
         DATA_DMORL_CD_07_celadm08
         DATA_DMORL_CD_08_celadm08
         DATA_DMORL_CD_09_celadm08
         DATA_DMORL_CD_10_celadm08
         DATA_DMORL_CD_11_celadm08
         DBFS_DG_CD_02_celadm08
         DBFS_DG_CD_03_celadm08
         DBFS_DG_CD_04_celadm08
         DBFS_DG_CD_05_celadm08
         DBFS_DG_CD_06_celadm08
         DBFS_DG_CD_07_celadm08
         DBFS_DG_CD_08_celadm08
         DBFS_DG_CD_09_celadm08
         DBFS_DG_CD_10_celadm08
         DBFS_DG_CD_11_celadm08
         RECO_DMORL_CD_00_celadm08
         RECO_DMORL_CD_01_celadm08
         RECO_DMORL_CD_02_celadm08
         RECO_DMORL_CD_03_celadm08
         RECO_DMORL_CD_04_celadm08
         RECO_DMORL_CD_05_celadm08
         RECO_DMORL_CD_06_celadm08
         RECO_DMORL_CD_07_celadm08
         RECO_DMORL_CD_08_celadm08
         RECO_DMORL_CD_09_celadm08
         RECO_DMORL_CD_10_celadm08
         RECO_DMORL_CD_11_celadm08

The number of dirty buffers (unflushed) will be 0 after flush is complete

CellCLI> LIST METRICCURRENT FC_BY_DIRTY

CellCLI> LIST METRICCURRENT FC_BY_DIRTY
         FC_BY_DIRTY     FLASHCACHE      0.000 MB

2. Drop the FlashCache

CellCLI> DROP FLASHCACHE all

3. Drop the FlashLog

CellCLI> DROP FLASHLOG all

4. Drop the celldisks on the FlashDisks

CellCLI> DROP CELLDISK all flashdisk

5. Enable flash cache compression using the following commands, based on the system:

If Exadata Storage Cell Server image is 11.2.3.3.0 and the Storage Cell is X3-2:

CellCLI> ALTER CELL flashCacheCompX3Support=true

CellCLI> ALTER CELL flashCacheCompress=true

If Exadata Storage Cell server image is 11.2.3.3.1 or higher:

CellCLI> ALTER CELL flashCacheCompress=true

6. Validate the Physical Disk/Luns have the new size (Reference Table 2. Physical Disk size for FlashDisks)

CellCLI>LIST PHYSICALDISK attributes name, physicalSize where disktype=flashdisk

	AURA 2.0 / F40/X3		AURA 2.1 / F80 / X4
	Compression OFF	Compression ON	Compression OFF	Compression ON
Physical Disk Size	93.13 G	186.26 G	186.26 G	372.53 G
Flash Cache Size	1489 G	2979 G	2979 G	5959 G

Table 1. Physical Disk size for FlashDisks

7. Create the celldisks on the FlashDisks

CellCLI> CREATE CELLDISK all flashdisk

Validate all sixteen FlashDisks are present

CellCLI> LIST CELLDISK where disktype=flashdisk

8. Create the FlashLog

CellCLI> CREATE FLASHLOG all

Validate FlashLog is in normal mode

CellCLI> LIST FLASHLOG detail

9.  Create the FlashCache

CellCLI> CREATE FLASHCACHE all

Validate FlashCache is in normal mode

CellCLI > LIST FLASHCACHE detail

How to disable Flash Cache compression:

 1. Flush the dirty blocks from Flash Disks to the GridDisks

CellCLI> ALTER FLASHCACHE all flush

To validate that flush operation was successful use any of following methods, opening a new cellcli session

Verify cachedby attribute is null.  If a FlashDisk is reported, flush is still in progress

CellCLI> LIST GRIDDISK attributes name,cachedby

The number of dirty buffers (unflushed) will be 0 after flush is complete

CellCLI> LIST METRICCURRENT fc_by_dirty

2. Drop the FlashCache

CellCLI> DROP FLASHCACHE all

3. Drop the FlashLog

CellCLI> DROP FLASHLOG all

4. Drop the celldisks on the FlashDisks

CellCLI> DROP CELLDISK all flashdisk

5. Disable Flash Cache Compression

If Exadata Storage Cell Server image is 11.2.3.3.0 and the Storage Cell is X3-2:

CellCLI> ALTER CELL flashCacheCompX3Support=true

CellCLI> ALTER CELL flashCacheCompress=false

If Exadata Storage Cell server image is 11.2.3.3.1 or higher:

CellCLI> ALTER CELL flashCacheCompress=false

 Validate it has been disabled by checking cell attributes:

CellCLI> LIST CELL attributes name,flashCacheCompress

Correct values are FALSE or a null string.

6. Validate the Physical Disks have been shrunk

CellCLI> LIST PHYSICALDISK attributes name,physicalSize, status where disktype=flashdisk

The status should be normal.  

Use the following table to validate the expected size when Compression is OFF

	AURA 2.0 / F40/X3		AURA 2.1 / F80 / X4
	Compression OFF	Compression ON	Compression OFF	Compression ON
Physical Disk Size	93.13 G	186.26 G	186.26 G	372.53 G
Flash Cache Size	1489 G	2979 G	2979 G	5959 G

 Table 2.PhysicalDisk size for FlashDisks

 7. Create the celldisks on the FlashDisks

CellCLI> create celldisk all flashdisk

Validate all sixteen FlashDisks are present

CellCLI> list celldisk where disktype=flashdisk

8. Create the FlashLog

CellCLI> create flashlog all

Validate FlashLog is in normal mode

CellCLI> list flashlog detail

9.  Create the FlashCache

CellCLI> create flashcache all

Validate FlashCache is in normal mode

CellCLI > list flashcache detail

Enable Exadata Flash Cache Compression – Non-Rolling Method

Create a cell_group file with other storage cell name

·  cat cell_group

    Storage server1

    Storage server2

·  dcli -g cell_group -l root cellcli -e list flashcache attributes size

·  dcli -g cell_group -l root cellcli -e alter flashcache all flush

·  dcli -g cell_group -l root cellcli -e drop flashcache all

·  dcli -g cell_group -l root cellcli -e drop flashlog all

·  dcli -g cell_group -l root cellcli -e drop celldisk all flashdisk

     

    For Exadata Storage Software version 11.2.3.3.1 & above and Exadata X4

    dcli -g cell_group -l root cellcli -e alter cell FlashCacheCompress=true

    For Exadata Storage Software version 11.2.3.3.0 and Exadata X3

   dcli -g cell_group -l root cellcli -e alter cell flashCacheCompX3Support=true

   dcli -g cell_group -l root cellcli -e alter cell flashCacheCompress=true

   dcli -g cell_group -l root cellcli -e create celldisk all flashdisk

   dcli -g cell_group -l root cellcli -e create flashlog all size=512M

   dcli -g cell_group -l root cellcli -e create flashcache all

   dcli -g cell_group -l root cellcli -e list cell attributes flashCacheCompress

   

   Note: Exadata Flash Cache Compression is discontinued for Exadata Storage Server X5.

   Reference: Oracle support Document (ID 1664257.1)