Background
Before we start if you are new to the Oracle ASM Filter Driver (ASMFD) you may want to visit a couple of my previous Blog posts where I detailed how to set-up the ASM Filter Driver (ASMFD) via Oracle 19c Grid Infrastructure installer or the Linux command line interface (CLI).
In this Blog I am going to show the impact of the Oracle ASM Filter Driver (ASMFD) ‘Thin Provisioning’ flag on flash stoarge.
Oracle ASM Diskgroup Set-up
For my testing I have created 3 PDB’s 3 additional Oracle ASM Disk Groups each with 3 volumes thus:
- pdb1- DATA_UDEV (Traditional UDEV managed)
- pdb2 – DATA_TP (ASM Filter Driver initial thin_provisioned=true )
- pdb3 – DATA_AFD (ASM Filter Driver initial thin_provisioned=false )
[oracle@z-oracle ~]$ asmcmd lsdsk -p -G DATA_UDEV Group_Num Disk_Num Incarn Mount_Stat Header_Stat Mode_Stat State Path 4 0 4042632098 CACHED MEMBER ONLINE NORMAL /dev/oracleasm/dg_oradata7 4 1 4042632097 CACHED MEMBER ONLINE NORMAL /dev/oracleasm/dg_oradata8 4 2 4042632096 CACHED MEMBER ONLINE NORMAL /dev/oracleasm/dg_oradata9
[oracle@z-oracle ~]$ asmcmd lsdsk -p -G DATA_AFD Group_Num Disk_Num Incarn Mount_Stat Header_Stat Mode_Stat State Path 5 0 4042632172 CACHED MEMBER ONLINE NORMAL AFD:DATA_AFD1 5 1 4042632173 CACHED MEMBER ONLINE NORMAL AFD:DATA_AFD2 5 2 4042632174 CACHED MEMBER ONLINE NORMAL AFD:DATA_AFD3
[oracle@z-oracle ~]$ asmcmd lsdsk -p -G DATA_TP Group_Num Disk_Num Incarn Mount_Stat Header_Stat Mode_Stat State Path 6 0 4042632212 CACHED MEMBER ONLINE NORMAL AFD:DATA_TP1 6 1 4042632213 CACHED MEMBER ONLINE NORMAL AFD:DATA_TP2 6 2 4042632214 CACHED MEMBER ONLINE NORMAL AFD:DATA_TP3
From the operating system it’s possible to determine the physical volume for and ASM Filter Driver diskgroup by navigating to ‘/dev/oracleafd/disks’ and reading the files e.g.
[oracle@z-oracle disks]$ cd /dev/oracleafd/disks
[oracle@z-oracle disks]$ ls -l
total 32
-rw-r----- 1 oracle oinstall 26 Oct 17 13:36 CONTROL_REDO1
-rw-r----- 1 oracle oinstall 24 Oct 28 21:33 DATA_AFD1
-rw-r----- 1 oracle oinstall 24 Oct 28 21:33 DATA_AFD2
-rw-r----- 1 oracle oinstall 24 Oct 28 21:33 DATA_AFD3
-rw-r----- 1 oracle oinstall 24 Oct 28 21:34 DATA_TP1
-rw-r----- 1 oracle oinstall 24 Oct 28 21:34 DATA_TP2
-rw-r----- 1 oracle oinstall 24 Oct 28 21:34 DATA_TP3
-rw-r----- 1 oracle oinstall 25 Oct 17 13:35 FRA1
[oracle@z-oracle disks]$ cat DATA_AFD1
/dev/mapper/dg_oradata1If we check our newly labeled ASM volumes we can see a few MB of data has been written to each volume header.
ASMFD Thin Provisioned Attribute
By default the ‘thin_provisioned’ flag is FALSE, even for ASMFD managed disks, we can check this with:
set feed off set pages 100 set linesize 250 column diskgroup heading 'Diskgroup' format a15 column name heading 'Attribute Name' format a25 column value heading 'Value' format a15 column read_only heading 'Read Only' format a15 SELECT SUBSTR(dg.name,1,12) AS diskgroup, SUBSTR(a.name,1,24) AS name, SUBSTR(a.value,1,24) AS value, read_only FROM V$ASM_DISKGROUP dg, V$ASM_ATTRIBUTE a WHERE dg.group_number = a.group_number AND a.name NOT LIKE '%template%' AND a.name LIKE '%thin%' / exit
However we can easily change the ‘thin_provisioned’ attribute using ASMCA or using ‘alter disk group <DISK_GROUP> set attribute ‘thin_provisioned’=’TRUE’;’ e.g.
[oracle@z-oracle ~]$ sqlplus / as sysasm
SQL> alter diskgroup DATA_TP set attribute 'thin_provisioned'='TRUE';
Diskgroup altered.
Create Test Data
To understand the impact of ‘thin_provisioning’ flag we will now create 3 empty Tablespaces each of 1TB in each or my PDB’s using three different ASM disk groups and then use Dominic Giles’ SwingBench to create SOE schemas in each of the new Tablespaces ~320GB.
Container Tablespace Free Alloc Used
CON_ID Name Name Space GB Space GB Space GB
---------- --------------- --------------- -------- -------- --------
3 PDB1 SOE 703 1,024 321 (UDEV, TP=FALSE)
4 PDB2 SOE 703 1,024 321 (ASMFD, TP=TRUE)
5 PDB3 SOE 703 1,024 321 (ASMFD, TP=FALSE) The screen shot below shows the updated 3 ASM DiskGroups.
Test 1 – Remove data from pdb2
To explore the impact of the ‘thin_provisioned’ attribute we can now drop the test data from our ASMFD labeled diskgroup and monitor the storage platform to see if any storage is returned.
SQL> drop user soe cascade;
User dropped.
SQL> drop tablespace soe including contents;
Tablespace dropped.Oracle ASM Rebalance
The Oracle documentation tells us that the ‘thin_provisioned‘ attribute only discards unused storage space after a disk group rebalance is completed, so we will need to also trigger a rebalance.
[oracle@z-oracle ~]$ sqlplus / as sysasm
SQL> alter diskgroup DATA_TP rebalance with balance compact wait;
Diskgroup altered.The ‘wait’ keyword can be useful in scripts as this ensures the rebalance function completes before returning.
Test 2 – Remove data from pdb3
In our second test we will update the ‘thin_provisioned’ attribute to ‘TRUE’ and repeat the same test, again monitoring the storage platform to see if data needs to be created with an initial thin_provisioned value of true to have any impact.
[oracle@z-oracle ~]$ sqlplus / as sysasm
SQL> alter diskgroup DATA_AFD set attribute 'thin_provisioned'='TRUE';
Diskgroup altered.
SQL> drop user soe cascade;
User dropped.
SQL> drop tablespace soe including contents;
Tablespace dropped.[oracle@z-oracle ~]$ sqlplus / as sysasm
SQL> alter diskgroup DATA_AFD rebalance with balance compact wait;
Diskgroup altered.
Test 3 – Remove data from pdb1
In our final test we repeat the above tests and check to see if setting the ‘thin_provisioned’ attribute to ‘TRUE’ for a UDEV managed Oracle ASM diskgroup releases any storage space.
[oracle@z-oracle ~]$ sqlplus / as sysasm
SQL> alter diskgroup DATA_UDEV set attribute 'thin_provisioned'='TRUE';
Diskgroup altered.
[oracle@z-oracle ~]$ sqlplus / as sysdba
SQL> drop user soe cascade;
User dropped.
SQL> drop tablespace soe including contents;
Tablespace dropped.[oracle@z-oracle ~]$ sqlplus / as sysasm
SQL> alter diskgroup DATA_UDEV rebalance with balance compact wait;
Diskgroup altered.
Conclusion
If your using Oracle Automatic Storage Management (ASM) with an all-flash storage platform should definitely put some time aside and test the Oracle ASM Filter Driver (ASMFD) in your environment.
For Oracle ASM Filter Driver labeled diskgroups you can update the ‘thin_provisioned’ attribute after the data created was initially created and still release space.
Please note setting it’s possible to set the ‘thin_provisioned’ attribute to ‘TRUE’ for UDEV managed Diskgroups but it will not release storage space.
If you have found this Post informative you may want to check out my video of ASMFD in action.
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