Dell Storage with Microsoft Storage Spaces Best Practices Guide

Storage Spaces automatically rebuilds VDs by using free disk space and does not require assigning hot-spares. If a physical disk fails, Storage Spaces regenerates the failed physical disk from free storage disk space without any user’s intervention. This means that the rebuild begins immediately limiting the exposure to additional physical disk failure while the VD is already running in a degraded state.

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

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