Oracle 11gR2 introduced the ability to change the redo log block size from its default 512 bytes to 4 KB. One reason was because certain drives used 4 KB as their native block size (for example, SSD drives). Another reason was to reduce the metadata overhead that was associated with high density Hard Disk Drives (HDD) by increasing the block size from its legacy 512 bytes to 4 KB.
When using PowerMax storage, there are two key reasons why the redo log block size should not be changed from the default 512 bytes per sector:
- The database never writes directly to the flash drives. Instead, all writes to the PowerMax storage system go to the PowerMax cache, where they can be aggregated to provide optimized writes to the flash media at a later time. Therefore, such a change does not benefit the drives directly.
- There is an increase in redo wastage that is often significant. When the Oracle database commits frequently, it requires an immediate write of the log buffer. With 4 KB blocks and frequent commits, the redo log buffer may be mostly empty, creating unnecessary write overhead and redo wastage.