March 16, 2018

ODA Xx – Space Waste When Using ACFS (instead of ASM) For Databases



Disclaimer: I will not discuss the necessity of an ACFS FS to store database files, nor compare ASM and ACFS or it's benefits. What to use / what fits best in Your environment is up to You, folks … ;-)

Pretty sure that this is for lots of people a well-known problem – but for all others:

When creating a database using ACFS as storage option, a FS of size 100GB is created. This 100GB is not a configurable value, by the way. Result is: When having lots of small databases, making use of ACFS wastes a lot of disk space, as every database's file system occupies 100GB.
Oracle Support's answer to that is: "In the future releases you may see the customized option to define the size of ACFS while creating the database". Nevertheless: It is possible to reduce that 100GB FS to an appropriate size. Here's how:  

Examples are based on OAK 12.2.1.2.0, used db release: 12.1.0.2

Create the database:

oracle@eoda03 ~]$ odacli create-database -m -n RCRACFS1 --no-cdb  --dbstorage ACFS -dh cce28d1b-01cc-4917-8237-38683d34f53e

… results in (from a FS perspective)

Filesystem                   Size  Used Avail Use% Mounted on
/dev/asm/datrcracfs1-262     100G  2.5G   98G   3% /u02/app/oracle/oradata/RCRACFS1

Reduce the filesystem size to 10GB:

[oracle@eoda03 ~]$ acfsutil size -90G /u02/app/oracle/oradata/RCRACFS1
acfsutil size: new file system size: 10737418240 (10240MB)

Check the filesystem size

[oracle@oda03 ~]$ df -h /u02/app/oracle/oradata/RCRACFS1
Filesystem                   Size  Used Avail Use% Mounted on
/dev/asm/datrcracfs1-262      20G  2.5G   18G  13% /u02/app/oracle/oradata/RCRACFS1

20G?? 100 minus 90 is 20? Possibly yes (you never know ;-)) – on the other hand and a better explanation: 20GB could be minimum FS for an ACFS file system.

Conclusion:

Yes! It is that easy J

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