Fastpath; Configuring Fastpath-Capable Virtual Disks; Virtual Disk Migration - Dell PowerEdge VRTX User Manual

FastPath

FastPath is a feature that improves application performance by delivering high I/O per second (IOPS). The Shared PERC
8 card supports FastPath in non-VMware systems.
FastPath is a further enhancement of the Cut Through IO (CTIO) feature, introduced in earlier PERC cards. FastPath is
used to accelerate I/O performance by reducing the I/O processing overhead of the firmware. CTIO reduces the
instruction count required to process a given I/O. It also ensures that the optimal I/O code path is placed close to the
processor to allow faster access when processing the I/O.
Under specific conditions with FastPath, the I/O bypasses the controller cache and is committed directly to the physical
disk from the host memory, through the second core of the dual-core RAID-on-Chip (ROC) on the controller. FastPath
and CTIO are both ideal for random workloads with small blocks.
Both CTIO and FastPath provide enhanced performance benefits to SAS SSD volumes, as they can fully capitalize on the
lower access times and latencies of these volumes.
FastPath provides I/O performance benefits to rotational HDD-based volumes configured with Write Through and No
Read Ahead cache policies, specifically for read operations across all RAID levels and write operations for RAID 0.

Configuring FastPath-Capable Virtual Disks

All simple virtual disks configured with write-cache policy Write Through and read-cache policy No Read Ahead can
utilize FastPath. Only I/O block sizes smaller than virtual disk's stripe size are eligible for FastPath. In addition, there must
be no background operations (rebuild, initialization) running on the virtual disks. FastPath is not used if these operations
are active.
NOTE: RAID 10, RAID 50, and RAID 60 virtual disks cannot use FastPath.
The following table summarizes the FastPath-eligibility of read and write I/Os across the supported RAID levels.
Table 2. FastPath Eligibility Across Supported RAID Levels
RAID 0
Read Yes
Write Yes

Virtual Disk Migration

The Shared PERC 8 card supports migration of virtual disks from one controller to another without taking the target
controller offline. The controller can import RAID virtual disks in optimal, degraded, or partially degraded states. You
cannot import a virtual disk that is in a failed state. Virtual disk migration:
• Supports migration of virtual disks from a similar Shared PERC 8 card.
• Does not support migration from any other PERC cards such as PERC H310, H700, H710, H800, and H810.
• Does not support Non-RAID disks.
NOTE: You must turn off the source system before you perform the disk migration.
When a controller detects a physical disk with an existing configuration, it flags the physical disk as a foreign disk and
generates an alert indicating that a foreign disk was detected.
RAID 1 RAID 5
Yes Yes
(Optimal and (Optimal and Degraded)
Degraded)
No No
RAID 6
Yes
(Optimal and Degraded)
No
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