Rebalance; Rebalance Throttling - Dell EMC VxFlex Ready Node User Manual
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Rebalance
Rebalance throttling
either threshold is reached, the rebuild I/Os wait until both I/O and bandwidth are
below their thresholds. For example, setting the value to "1" will guarantee the
device will only have one concurrent rebuild IO at any given moment, which will
ensure the application IOs only wait for 1 rebuild IO at worst case.
This imposes bandwidth on top of the Limit Concurrent I/Os option, which is a
prerequisite to using this policy.
Dynamic Bandwidth Throttling: This policy is similar to Favor Application I/O, but
l
extends the interval in which application I/Os are considered to be flowing by
defining a minimal quiet period. This quiet period is defined as a certain interval in
which no application I/Os occurred. Note that the limits on the rebuild bandwidth
and concurrent I/Os are still imposed.
Default Values:
l
The default policy for rebuild is: Limit Concurrent I/O
n
Rebuild concurrent I/O Limit: 1 concurrent I/O
n
Note:
Rebuild throttling affects the system's performance and should only be
used by advanced users.
When VxFlex OS detects that user data is not balanced across devices in the Storage
Pool, it initiates a process to restore the balance in which data copies are moved from
the most utilized devices to the least utilized.
Rebalance is the process of moving one of the data copies to a different server. It
occurs when VxFlex OS detects that the user data is not evenly balanced across the
devices in a Storage Pool. This can occur as a result of several conditions such as:
SDS addition/removal, device addition/removal, or following a recovery from a failure.
VxFlex OS will move copies of the data from the most utilized devices to the least
utilized ones.
Both Rebuild and Rebalance compete with the application IO for the system
resources. This includes network, CPU and disks. VxFlex OS provides a very rich set
of parameters that can control this resource consumption. While the system is
factory-tuned for balancing between speedy rebuild/rebalance and minimization of
the effect on the application IO, the user has very fine-grain control over the rebuild
and rebalance behavior.
The rebalance throttling policy determines the priority of rebalance I/Os versus
application I/Os when accessing SDS devices. The possible rebuild throttling policies
are no limit on rebalance I/Os, limit concurrent I/Os per SDS device, Favor application
I/Os and Dynamic Bandwidth Throttling.
Rebalance throttling sets the rebalance priority policy for a Storage Pool. The policy
determines the priority between the rebalance I/O and the application IO when
accessing SDS devices. Please note that application I/Os are continuously served.
Rebalance, unlike rebuild, does not impact the system's reliability and therefore
reducing its impact is not risky.
Note:
Rebalance throttling affects the system's performance and should only be used by
advanced users.
The following possible priority policies may be applied:
Dell EMC VxFlex Ready Node AMS User Guide
Architecture
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