Quantum QX Series User Manual

Chapter 1: Components
Component Installation and Replacement
QX and QXS Setup Guide 47
Component Installation and Replacement
Installation and replacement of QXS Storage components is addressed in the QXS Storage CRU
Installation and Replacement.
CRU procedures facilitate replacement of a damaged chassis or chassis components:
l Controller or expansion module
l Drive module
l Drawer (QXS-456)
l Power supply unit
l Fan control unit
l Ear bezels
l FC transceiver
l RAID chassis
Cache
To enable faster data access from storage, the following types of caching are performed:
l Write-back or write-through caching.
l Write-back. The controller receives the data to be written to drives, stores it in the memory buffer,
and immediately sends the host operating system a signal that the write operation is complete,
without waiting until the data is actually written to the drive. Write-back cache mirrors all of the data
from one controller module cache to the other. Write-back cache improves the performance of write
operations and the throughput of the controller.
l Write-through. The controller writes the data to the drives before signaling the host operating
system that the process is complete. Write-through cache has lower write operation and throughput
performance than write-back, but it is the safer strategy, with minimum risk of data loss on power
failure. However, write-through cache does not mirror the write data, because the data is written to
the drive before command completion is posted and mirroring is not required.
l Read-aheadcaching. The controller detects sequential data access, reads ahead into the next
sequence of data (based upon settings) and stores the data in the read-ahead cache. Then, if the next
read access is for cached data, the controller immediately loads the data into the system memory,
avoiding the latency of a drive access.
Note:See the “About volume cache options” and “Changing system cache settings” topics in the
Quantum Disk Storage Management Utility Users Guide for setting options.

Quantum QX Series Specifications

General

Brand	Quantum
Model	QX Series
Category	Storage
Language	English