About Flash Cache; Flash Cache Module; How Flash Cache Works - IBM N Series Hardware Manual

12.1 About Flash Cache

Flash Cache (previously called PAM II) is a set of solutions that combine software and
hardware within IBM N series storage controllers. It increases system performance without
increasing the disk drive count. Flash Cache is implemented as software features in Data
ONTAP and PCIe-based modules with either 256 GB, 512 GB, or 1 TB of flash memory per
module. The modules are controlled by custom-coded Field Programmable Gate Array
processors. Multiple modules can be combined in a single system and are presented as a
single unit. This technology allows submillisecond access to data that would previously have
been served from disk at averages of 10 milliseconds or more.
Tip: This solution is suitable for all types of workloads, but provides the greatest benefit
from IBM System Storage N series storage subsystems that serve intensive random read
transactions.

12.2 Flash Cache module

The Flash Cache option offers a way to optimize the performance of an N series storage
system by improving throughput and latency. It also reduces the number of disk
spindles/shelves required, and the power, cooling, and rack space requirements.
A Flash Cache module provides an additional 256 GB, 512 GB, or 1 TB (PAM II) of extended
cache for your IBM System Storage N series storage subsystem. The amount depends on the
model. Up to eight modules can be installed. Each module must be installed on a PCI express
slot, and consumes only an additional 18 W of power per module. Extra rack space and
ventilation are not required, making it an environmentally friendly option. Figure 12-1 shows
the Flash Cache module.
Figure 12-1 Flash Cache Module

12.3 How Flash Cache works

Flash Cache replaces disk reads with access to an extended cache contained in one or more
hardware modules. Your workload is accelerated in direct proportion to the disk reads
replaced. The remainder of this document focuses on different workloads and how they are
accelerated. It also covers how to choose and configure the best mode of operation, and how
to observe Flash Cache at work.
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IBM System Storage N series Hardware Guide