Dot Hill Systems AssuredSAN 4544, Setup Manual

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AssuredSAN Ultra48 Series Setup Guide 21
• Replacing a power supply unit with integrated cooling fans.
• Replacing ear components
• Replacing a Fibre Channel transceiver
• Replacing a 10GbE SFP+ transceiver
• Replacing a 1 Gb SFP transceiver
• Replacing a controller enclosure chassis
See Dot Hill’s Customer Resource Center web site for additional information: http://crc.dothill.com .
Select AssuredSAN & R/Evolution Products > Ultra48 Series to download the FRU I&R guide.
Cache
To enable faster data access from disk storage, the following types of caching are performed:
• Write-back or write-through caching. The controller writes user data into the cache memory in the
controller module rather than directly to the disks. Later, when the storage system is either idle or aging
—and continuing to receive new I/O data—the controller writes the data to the disks.
• 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 disk access.
TIP: See the “About volume cache options” and “Changing system cache settings” topics in the RAIDar
User Guide for setting options.
CompactFlash
During a power loss or controller failure, data stored in cache is saved off to non-volatile memory
(CompactFlash). The data is restored to cache, and then written to disk after the issue is corrected. To
protect against writing incomplete data to disk, the image stored on the CompactFlash is verified before
committing to disk.
The CompactFlash card is located at the midplane-facing end of the controller module as shown in
Figure 10 on page 22. Do not remove the card; it is used for cache recovery only.
IMPORTANT: Customer removal of CompactFlash will void the product warranty.
IMPORTANT: In dual-controller configurations featuring one healthy partner controller, there is no need to
transport failed controller cache to a replacement controller because the cache is duplicated between the
controllers (subject to volume write optimization setting).
IMPORTANT: The Ultra48 Series enclosures support dual-controller environments only. Do not transport
the CompactFlash since data corruption might occur. Single-controller support is provided only when a
controller fails over to its partner controller.