Users Guide

Dell recommends you to assign the storage solution to allow for automatic rebuilds.
Run the following PowerShell command to enable automatic rebuilds (configured for each pool).
Set-StoragePool –FriendlyName <poolName> -RetireMissingPhysicalDisks Always
NOTE: Before performing maintenance operations (when storage pools are configured to
automatically rebuild), you must turn off the storage enclosure. Also, you must change the
RetireMissingPhysicalDisks attribute of all affected storage pools to Never. Changing this
prevents the VDs from initiating rebuilds because of a perceived failure when the storage enclosure
is turned off for maintenance. Ensure that you change RetireMissingPhysicalDisks back to
the original value after the maintenance operation is complete.
When you configure a storage pool to automatically rebuild, you must reserve enough free disk space in
each pool such that VDs can automatically rebuild when a physical disk failure occurs. Maintain sufficient
free disk space in each of the storage pools which is equal to 10 percent of the available HDD disk space
for the HDD tier, and 10 percent of the SSD disk space for the SSD tier. Equations for sizing the HDD and
SSD tiers while accounting for the 10 percent are specified in the Storage Tiers section in this document.
There are two types of rebuild methods — parallel and sequential. During a parallel rebuild process, the
data required to rebuild is obtained from multiple physical disks in the pool. Parallel rebuilds are very fast
and reduce the time a VD is in a degraded state. However, multiple physical disks are sourcing the repair
data there is some impact to normal I/O during rebuilds. A sequential rebuild only sources repair data
from one physical disk in the pool at a time. This means that there is less impact to normal I/O during
rebuilds, however, the rebuild process takes a much longer time.
Dell recommends parallel rebuilds because it provides the fastest method to ensure all VDs return to their
full resiliency. To optimize VD repairs the Microsoft November 2014 KB rollup (KB3000850) is required on
all storage nodes. Also, you must perform the steps listed in this Microsoft article on each storage node:
https://technet.microsoft.com/en-us/library/dn858079.aspx
Run one of the following PowerShell commands for configuring the rebuild method (configured for each
pool).
Set-StoragePool –FriendlyName <poolName> –RepairPolicy Parallel
Set-StoragePool –FriendlyName <poolName> –RepairPolicy Sequential
Virtual disks (Storage Spaces)
When you configure a VD, there is an option to select from various resiliency types — simple, Two-way
mirror, three-way mirror, single parity, or dual parity.
Dell recommends you to use two-way or three-way mirror VDs. Mirrored VDs are optimized and provide
the best performance and resiliency for Hyper-V workloads.
Parity VDs are intended for workloads which are sequential, such as backup and archiving. Do not use
parity VDs for random workloads, because this impacts performance.
Simple VDs are not recommended, because they provide no resiliency.
15