Oracle Exadata represents the most capable and powerful converged system on the planet for consumer businesses. While most people are familiar with flash cache and storage cells, Cintra occasionally runs into a few features with which even the most experienced Database Machine Administrators are not familiar. Here are a list of some that we typically address as part of our optimization services.
“appliance.mode” is an ASM disk group attribute which improves disk rebalancing times so that redundancy is restored much faster after a disk drop or addition operation, or after a drive failure.
Database Machine Administrators who have upgraded to Exadata release 126.96.36.199.0 (yes, it’s been available for a while!) can use this attribute. This needs to be set at the ASM level and can be set using traditional “alter diskgroup” SQL statements.
As with all the Oracle Features there are restrictions when setting this. Two key considerations are that compatible.asm must be set to 188.8.131.52 or higher on the disk group, and cell.smart_scan_capable must be set to TRUE.
With Oracle Grid Infrastructure 184.108.40.206, Oracle introduced a new parameter “content.type” for ASM which takes 3 different values: data, recovery and system. Each type of setting modifies the adjacency measure used by Exadata’s secondary extent placement algorithm.
Using these settings, the likelihood of a double failure (in a “normal” redundancy ASM diskgroup) which could result in data loss, is reduced. Enabling this attribute requires rebalancing of the diskgroup, and therefore it makes sense to perform this change outside of busy times.
The explanation of these features would require a dedicated blog, so if you would like to learn more please get in contact with us.
Also in Exadata release 220.127.116.11.0, Oracle introduced an automatic hard disk scrub and repair function, where disks are scanned for latent corruptions.
This I/O scrub operation only happens when disks are idle, avoiding any impact on database workloads. However, it is still a good idea to schedule the hard disk scrub for a time when the system is most idle and there is less activity going on.
Better Security for Cell Servers
With the latest Exadata release at the time of writing, 18.104.22.168.0, it is possible to completely disable ssh on cell servers. The obvious question is then how do you access the storage cells? Oracle, as the tradition goes, provided another utility with this release, ExaCli, which can be invoked from the Compute Nodes. It is possible to run cellcli commands using this utility without direct access to the storage servers.
This utility can also be used to create windows for enabling ssh to the Storage Servers, allowing us to enable ssh for times when we it may be needed for patching or maintenance operations.
For more information on these and many more Exadata features, contact Cintra today!
Written by Vineet Sachdeva, Oracle DBA, Cintra India