Dell PowerEdge RAID Controller H710 - Manual (Page 15)

Disk Roaming
Disk roaming is moving the physical disks from one cable connection or backplane slot to another on the same
controller. The controller automatically recognizes the relocated physical disks and logically places them in the virtual
disks that are part of the disk group. You can perform disk roaming only when the system is turned off.
CAUTION: Do not attempt disk roaming during RAID level migration (RLM) or online capacity expansion (OCE). This
causes loss of the virtual disk.
Using Disk Roaming
Perform the following steps to use disk roaming:
1. Turn off the power to the system, physical disks, enclosures, and system components.
2. Disconnect power cables from the system.
3. Move the physical disks to desired positions on the backplane or the enclosure.
4. Perform a safety check. Make sure the physical disks are inserted properly.
5. Turn on the system.
The controller detects the RAID configuration from the configuration data on the physical disks.
FastPath
FastPath is a feature that improves application performance by delivering high I/O per second (IOPs). The Dell
PowerEdge RAID Controller (PERC) H710P and H810 cards support FastPath.
FastPath is a further enhancement of the Cut Through IO (CTIO) feature, introduced in PERC H700 and PERC H800, to
accelerate IO performance by reducing the IO processing overhead of the firmware. CTIO reduces the instruction count
required to process a given IO. It also ensures that the optimal IO code path is placed close to the processor to allow
faster access when processing the IO.
Under specific conditions with FastPath, the IO by-passes 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.
NOTE: The PERC H310 and PERC H710 do not support FastPath.
Both CTIO and FastPath provide enhanced performance benefits to SSD volumes, as they can fully capitalize on the
lower access times and latencies of these volumes.
FastPath provides IO 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 IO block sizes smaller than virtual disk’s stripe size are eligible for FastPath. In addition, there
should be no background operations (rebuild, initialization) running on the virtual disks. FastPath will not be 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 IOs across the supported RAID levels.
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