System Overview; Enclosure Configurations; Cache; Compactflash - Seagate RealStor 5005 Series Hardware Installation

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System overview

Enclosure configurations

The storage system supports two controller enclosure configurations.
• 2U (rack space) controller enclosure – see
high) 3.5" form factor disk drive modules in a horizontal orientation.
• 2U (rack space) controller enclosure – see
inch high) 2.5" form factor disk drive modules in a vertical orientation.
These same chassis form factors are used for supported expansion enclosures; albeit with different I/O modules (IOMs).
Each individual disk drive is hot pluggable and replaceable on site.
NOTE: Throughout this guide—and the management interfaces documents used with this guide—I/O module (IOM) is
a general term denoting either a controller module (RAID canister) or an expansion module (expansion canister).
The enclosure configurations—including chassis and CRUs—are described on the following pages.

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 Storage Management Guide for more information about cache options and settings.

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 memory card is
located at the midplane-facing end of the controller module. Do not remove the card; it is used for cache recovery only.
NOTE: In dual-controller configurations featuring one healthy partner controller, cache is duplicated between the
controllers (subject to volume write optimization setting).

Supercapacitor pack

To protect controller module cache in case of power failure, each controller enclosure model is equipped with
supercapacitor technology, in conjunction with CompactFlash memory, built into each controller module to provide
extended cache memory backup time. The supercapacitor pack provides energy for backing up unwritten data in the
write cache to the CompactFlash, in the event of a power failure. Unwritten data in CompactFlash memory is
automatically committed to disk media when power is restored. In the event of power failure, while cache is maintained
by the supercapacitor pack, the Cache Status LED blinks at a rate of 1/10 second on and 9/10 second off. See also
Status LED details" (page
16 System overview
Figure 1 (page 17)
Figure 3 (page 18)
30).
and Figure 2 (page 17): holds up to 12 low profile (1-inch
and Figure 4 (page 18): holds up to 24 low profile (5/8
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