Performance and Scalability Considerations for Disk Groups
Determining the Number of Disk Groups
Use the following criteria to determine the number of disk groups to create:
-
Disks in a given disk group should have similar size and performance characteristics. If you have several different types of disks in terms of size and performance, then create several disk groups that contain similar characteristics.
-
Create separate disk groups for your database files and fast recovery area for backup files. This configuration allows fast recovery should a disk group failure occur.
For information about creating disk groups for a new installation, refer to Creating Disk Groups for a New Oracle Installation.
Performance Characteristics When Grouping Disks
Oracle ASM load balances the file activity by uniformly distributing file extents across all of the disks in a disk group. For this technique to be effective it is important that disks in a disk group be of similar performance characteristics. For example, the newest and fastest disks might reside in a disk group reserved for the database work area, and slower drives could reside in a disk group reserved for the fast recovery area.
There might be situations where it is acceptable to temporarily have disks of different sizes and performance characteristics coexist in a disk group. This would be the case when migrating from an old set of disks to a new set of disks. The new disks would be added and the old disks dropped. As the old disks are dropped, their storage is migrated to the new disks while the disk group is online.
Oracle ASM Storage Limits
Oracle ASM provides near unlimited capacity for future growth, but does have some storage limits.
Oracle ASM has the following limits on the number of disk groups, disks, and files:
-
511 disk groups in a storage system for Oracle Database 12c Release 1 or later
-
10,000 Oracle ASM disks in a disk group
-
65,530 Oracle ASM disks in a storage system
-
1 million files for each disk group
Without any Oracle Exadata Storage, Oracle ASM has the following storage limits if the COMPATIBLE.ASM
or COMPATIBLE.RDBMS
disk group attribute is set to less than 12.1
:
-
2 terabytes (TB) maximum storage for each Oracle ASM disk
-
20 petabytes (PB) maximum for the storage system
Without any Oracle Exadata Storage, Oracle ASM has the following storage limits if the COMPATIBLE.ASM
and COMPATIBLE.RDBMS
disk group attributes are set to 12.1
or greater:
-
4 PB maximum storage for each Oracle ASM disk with the allocation unit (AU) size equal to 1 MB
-
8 PB maximum storage for each Oracle ASM disk with the AU size equal to 2 MB
-
16 PB maximum storage for each Oracle ASM disk with the AU size equal to 4 MB
-
32 PB maximum storage for each Oracle ASM disk with the AU size equal to 8 MB
-
320 exabytes (EB) maximum for the storage system
With all Oracle Exadata Storage, Oracle ASM has the following storage limits:
-
4 PB maximum storage for each Oracle ASM disk with the AU size equal to 1 MB
-
8 PB maximum storage for each Oracle ASM disk with the AU size equal to 2 MB
-
16 PB maximum storage for each Oracle ASM disk with the AU size equal to 4 MB
-
32 PB maximum storage for each Oracle ASM disk with the AU size equal to 8 MB
-
320 EB maximum for the storage system
The maximum size limit of a disk group equals the maximum disk size multiplied by the maximum number of disks in a disk group (10,000).
The maximum number of disks across all disk groups is 65,530 disks. However, the total number of disks that can be in one disk group is limited to 10,000 disks. This is a limitation on the number of Oracle ASM disks, not necessarily the number of physical storage devices. A storage array could group multiple physical storage devices into a LUN that is used as a single Oracle ASM disk.
File size limits are dependent on the value of the disk group compatibility attributes. Oracle ASM supports file sizes greater than 128 TB in any redundancy mode when the COMPATIBLE.RDBMS
disk group attribute is set greater than 10.1
.
If COMPATIBLE.RDBMS
is set to 10.1
, the file size limits are less. For example, with COMPATIBLE.RDBMS
equal to 10.1
and the AU size equal to 1 MB, Oracle ASM file size limits are:
-
External redundancy: 16 TB
-
Normal redundancy: 5.8 TB
-
High redundancy: 3.9 TB
Note:
Oracle Database supports data file sizes up to 128 TB depending on the file system. In addition, Oracle Database has a file size limit that is dependent on the DB_BLOCK_SIZE
initialization parameter.
See Also:
-
Disk Group Compatibility for information about Oracle ASM disk group compatibility attributes
-
Considerations When Setting Disk Group Compatibility for additional information about Oracle ASM file size limits
-
Oracle Advanced Cluster File System Administrator's Guide for information about Oracle ACFS space usage