Chapter 1: Components
Component Installation and Replacement
QX and QXS Setup Guide
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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:
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Controller or expansion module
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Drive module
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Drawer (QXS-456)
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Power supply unit
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Fan control unit
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Ear bezels
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FC transceiver
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RAID chassis
Cache
To enable faster data access from storage, the following types of caching are performed:
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Write-back or write-through caching.
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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.
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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.
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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.
