System Overview 45
• A 16Gb/s SFP can run at 16Gb/s, 8Gb/s, 4Gb/s, or auto-negotiate its link speed.
• An 8Gb/s SFP can run at 8Gb/s, 4Gb/s, or auto-negotiate its link speed.
•
2
When in 10GbE iSCSI mode, the SFPs must be a qualified 10GbE iSCSI optic option.
•
3
When powering up and booting, iSCSI LEDs will be on/blinking momentarily, then they will
switch to the mode of operation.
•
4
Cache Status LED supports power on behavior and operational (cache status) behavior.
•
5
When port is down, both LEDs are off.
Cache Overview and Status LED Details
This section provides the following information:
• Cache Overview
• Power On/Off Behavior
• Cache Status Behavior
Cache Overview
To enable faster data access from disk storage, the following types of caching are performed:
• Write-back 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
QXS G2 Disk Management Utility User Guide
for more information about cache options
and settings.
Power On/Off Behavior
The storage chassis unified complex programmable logic device (CPLD) provides integrated Power
Reset Management (PRM) functions. During power on, discrete sequencing for power on display
states of internal components is reflected by blinking patterns displayed by the Cache Status LED.
Tabl e 4 provides the cache status LED behavior.
Ta b l e 4 Cache Status LED – Power On Behavior
Item Display states reported by Cache Status LED during power on sequence
Display state01234567
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