Considerations for solid-state drives (SSD)
The purpose of this section is to cover important controller functions when using solid-state drives (SSD).
Hard disk drives (HDD) use a spinning magnetic platter to store data in magnetic fields in nonvolatile storage. SSDs are storage devices that use nonvolatile solid-state memory (usually flash memory) to emulate HDDs. HDDs have an inherent latency and access time caused by mechanical delays in the spinning of the platter and movement of the head. SSDs greatly reduce the latency and time to access the stored data. The nature of solid-state memory is such that read operations can be performed faster than write operations and that write cycles are limited. Using techniques such as wear leveling and overprovisioning, enterprise class SSDs are designed to withstand many years of continuous use.
- SSD usage specifications
While using SSDs, consider the following specifications:
- Intermixing of SSDs and HDDs within the same disk array is not allowed. A disk array must contain all SSDs or all HDDs.
- It is important to properly plan for hot-spare devices when using arrays of SSDs. An SSD hot-spare device is used to replace a failed device in an SSD disk array and an HDD hot spare is used for an HDD disk array
- Although SSDs can be used in a RAID 0 disk array, it is preferred that SSDs to be protected by RAID levels 5, 6, 10, 5T2, 6T2, or 10T2.
- See Installing and configuring Solid-state drives to identify specific configuration and placement requirements related to the SSD devices.
- Some adapters, known as RAID and SSD adapters, contain SSDs, which are integrated on the adapter. See the PCIe SAS RAID card comparison table for features and additional information for your specific adapter type.
- SSDs are supported only when formatted to a RAID block size and used as part of a RAID array.
- RAID 0 automatically created disk array on a PCIe or PCIe2 SAS RAID Controller
During the controller boot process, any 528 bytes per sector (not 4224 bytes per secotor) SSD array candidate attached to a PCIe or PCIe2 SAS RAID Controller that is not already part of a disk array is automatically created as a single-drive RAID 0 disk array. Following are the two options for changing the RAID 0 disk array to a protected RAID level:
- The RAID 0 disk array can be migrated to a RAID 10 disk array by using the technique described in Migrating an existing disk array to a new RAID level.
- The automatically created RAID 0 disk array can be deleted (see Deleting a disk array) and a new SSD disk array can be created with a different level of RAID protection (see Creating a disk array).
- Adapter cache control
Adapter caching improves overall performance with disk drives. In some configurations, adapter caching might not improve performance when you use SSD disk arrays. In these situations, adapter caching can be disabled by using the Change Configuration of Adapter window.
- Run the iprconfig utility by typing iprconfig.
- Select Work with adapter configuration.
- Select the desired adapter by typing 1, and press Enter.
- Select IOA Caching Mode.
- Type c.
- Select Disabled and press Enter. A display similar to the following example appears in the window.
+-------------------------------------------------------------------–-----–----–+
| Change configuration of Adapter |
| |
|Current Adapter configurations are shown. To change setting hit 'c' for options |
|menu. Highlight desired option then hit Enter. |
| c=Change Setting |
| |
| Adapter: 0001:00:01.0/33 IBM 574E001SISIOA |
| |
| Preferred Dual Adapter State . . . . . . : Primary |
| Active/Active Mode . . . . . . . . . . . : Enabled |
| IOA Caching Mode . . . . . . . . . . . . : Default |
| |
| |
| |
|Or leave blank and press Enter to cancel |
|e=exit q=cancel |
| |
+--------------------------------------------------------------------------------+
