Oracle/HP Best Practices Guide for HP IO Accelerators

Generic performance tuning 12
Generic performance tuning
Write performance and steady state
Solid state storage solutions often have poor right performance. This condition is caused by the
characteristics of the underlying storage media, NAND flash. As more data is written to a solid state
device, you must defragment the data on the device to continue operating. This process is called
grooming. When the groomer starts, the IO Accelerator (like other solid state storage) experiences a
reduction in sustained write performance and an increase in latency. This behavior is known, and the
industry solution is trim (also known as discard).
Trim enables a block device consumer (typically a filesystem) to notify the underlying device (such as an
IO Accelerator) that some portion of the data is no longer needed. The device can use this information to
improve grooming efficiency, thus improving the performance of the device while in steady state. But trim
is a new feature and has not yet been deployed on many enterprise operating systems. Applications such
as Oracle that allocate large files are not able to take advantage of trim, even when deployed on an
operating system that supports it.
Because of tight integration with the system, the IO Accelerator also provides a capability called under-
formatting. This feature is not available in solid state devices built on traditional storage protocols. By
under-formatting an IO Accelerator, you can trade the presented capacity (for example, take a 160GB
drive and present it as a 140GB drive) to achieve higher steady state write performance. For high-write
workloads, this option provides a combination of usable capacity and write performance, rather than
purchasing unnecessary capacity to achieve needed write performance.
Because of the write-intensive nature of databases, even in read-heavy environments, HP recommends
under-formatting to 70-80% of standard capacity as a good starting point for most Oracle deployments.
Under-formatting can be done through the HP IO Accelerator Management Tool or through the command-
line utility fio-format. For more details on formatting, see the User Guides for your operating system.
Separating data types
When hosting all or a combination of temporary, primary data area, and redo logs on IO Accelerators,
you can achieve additional performance by isolating those areas to individual drives. This benefit can be
accomplished by identifying the needed capacities and appropriate level of under-formatting for each
storage area.
For example:
1. Under-format the IO Accelerators to the appropriate level.
2. Create unique ASM disk groups/failure groups from the target IO Accelerators for each of the
storage areas.
You can take a similar approach if you are are using MD/LVM for device aggregation along with
filesystems for hosting the data. Then the appropriate level of under-formatting must be applied to each
target area, based on the workload.