Administrator Guide

Using SSD cache
The SSD cache feature uses solid-state disk (SSD) physical disks to improve read-only performance in your storage array. SSD physical
disks are logically grouped together to provide secondary cache for use with the primary cache in the RAID controller module memory.
Using SSD cache improves application throughput and response times and delivers sustained performance improvement across diverse
workloads, especially high-IOP workloads.
Topics:
• How SSD cache works
• Benefits of SSD cache
• Choosing SSD cache parameters
• SSD cache restrictions
• Creating an SSD cache
• Viewing physical components associated with an SSD cache
• Locating physical disks in an SSD cache
• Adding physical disks to an SSD cache
• Removing physical disks from an SSD cache
• Suspending or resuming SSD caching
• Changing I/O type in an SSD cache
• Renaming an SSD cache
• Deleting SSD cache
• Using the performance modeling tool
How SSD cache works
Following a host read, data is stored in DRAM and is copied from user-specified base virtual disks and stored on two internal RAID virtual
disks (one per RAID controller module). These virtual disks are automatically created when you initially set up an SSD cache. Neither virtual
disks is accessible for read-write operations and cannot be displayed or managed in the MD Storage Manager interface.
Simple virtual disk I/O mechanisms are used to move data to and from the SSD cache.
Storing the data on the SSD cache eliminates the need for repeated access to the base virtual disk. However, both SSD cache virtual
disks count against the number of virtual disks supported on the storage array.
Benefits of SSD cache
Benefits of using the SSD cache feature varies depending on your system configuration and network environment. However, workloads
that typically benefit the most from using high-performance SSD cache include:
• Workloads where performance is limited by physical disk input/output processes (IOPs).
• Applications that generate a much higher percentage of physical disk reads versus physical disk writes.
• Repeated reads to the same and/or adjacent areas of the physical disk.
• Overall data accessed by an application is routinely less than potential SSD cache capacity. To determine whether this is the case,
reviewing the number of virtual disks and sizes that are cached often yields a reliable estimate. The more virtual disks that are cached,
the more likely it is that your application accesses more data capacity than can be configured in SSD cache.
Choosing SSD cache parameters
When you create an SSD cache, you can choose which I/O type best matches your applications:
• file system
• database
• web server
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