Dell PowerVault ME5 Series Administrator's Guide

Optimizing read-ahead caching

You can optimize a volume for sequential reads or streaming data by changing its read-ahead cache settings.

You can change the amount of data read in advance. Increasing the read-ahead cache size can greatly improve performance for multiple sequential read streams.

• The Adaptive option works well for most applications: it enables adaptive read-ahead, which allows the controller to dynamically calculate the optimum read-ahead size for the current workload.
• The Stripe option sets the read-ahead size to one stripe. The controllers treat NRAID and RAID-1 disk groups internally as if they have a stripe size of 512 KB, even though they are not striped.
• Specific size options let you select an amount of data for all accesses. Options include 512 KB, 1 MB, 2 MB, 4 MB, 8 MB, 16 MB, 32 MB.
• The Disabled option turns off read-ahead cache. This is useful if the host is triggering read ahead for what are random accesses. This can happen if the host breaks up the random I/O into two smaller reads, triggering read ahead.