Dell Storage with Microsoft Storage Spaces Best Practices Guide

Storage tiers enable the mixing of HDDs and SSDs in one pool to take advantage of the faster SSDs maximizing IOPS and throughput by using the SSDs for the most frequently accessed data. Microsoft Microsoft Storage Spaces constantly analyzes data usage patterns and moves the most frequently used data from the HDD tier to the SSD tier to speed up access.

Microsoft Storage Spaces creates a heat map based on the frequency that the data is used. Once a day, an optimization process automatically runs and the most frequently accessed data (hot data) is moved to the SSD tier and less frequently accessed data (cold data) is moved to the HDD tier.

Because the data on the SSD tier is updated only once a day (by default), if required, you can manually optimize data by running the following PowerShell command.

defrag.exe /C /H /K /G

You must run this command on all nodes in the cluster, because it only optimizes the VDs owned by the node where the command was run.

When validating the performance of your solution, perform benchmarks over the course of several days to allow the SSD tier to optimize for your workload. Alternatively, you can manually optimize the SSD tier. Manually optimizing storage tier data using the command above generates a Storage Tier Optimization Report. The Storage Tier Optimization report provides data on the storage tier, which can be used to identify methods to optimize performance.

You may want the ability to permanently place a frequently used file on the SSD tier. For example, a frequently accessed VHDX file that requires low latency and high throughput. You can accomplish this by pinning files to the SSD tier.

Even after pinning the file, it will not move to the SSD tier until the next optimization (or if you run it manually).

Dell recommends you to use pin sparingly, because the primary goal of storage tiers is to allow the heat map process to optimize the tiers.

Run the following Powershell command to pin files to the SSD tier.

Set-FileStorageTier –FilePath <localFilePath> 
                                    -DesiredStorageTierFriendlyName<ssdTierName>
                                 

Run the following Powershell command to unpin files from the SSD tier.

Set-FileStorageTier –FilePath <localFilePath>

Run the following PowerShell command to review all files currently pinned.

Get-FileStorageTier –VolumePath <csvVolumePath>

For example, pinning a VHDX file called myVHDX, which is on exampleShare on a CSV labeled Volume3. The storage tier is called MyPool1_SSD.

Set-FileStorageTier –FilePath “C:\ClusterStorage\Volume3\Shares\exampleShare\myVHDX.vhdx” –DesiredStorageTierFriendlyName
                                    “MyPool1_SSD”
                                 

Storage tiers are configured for each storage pool and it is recommended to create one SSD tier and one HDD tier for each storage pool.

The following equations are for planning purposes, when you start creating VDs in your storage pools. The values from the equations are used to understand the upper limit for capacity planning so that you are always leaving sufficient HDD and SDD raw disk space free across the pool as you create and size each VD for automatic rebuilds. These are not intended to be equations to guide you about sizing the tiers of the individual VDs. If you are not using automatic rebuilds and plan to only perform manual rebuilds, subtracting the capacity for automatic rebuilds in the equations below is not required..

Raw HDD Usable Capacity Per Pool=(Number of HDDs in the pool*HDD Capacity)-(HDD Capacity+8 GB for automatic rebuild space)*(Number of disk failures to recover from)

Tier size is the raw value modified by a resiliency factor depending on the type of Storage Space you are creating. For example, 1 for a Simple Space, 1/2 for a two-way Mirror, and 1/3 for a three-way mirror.

SSD Tier Per Pool= Raw SSD Usable Capacity Per Pool

HDD Tier Per Pool=Raw HDD Usable Capacity Per Pool

For example, a pool is created with 48 x 4 TB and 12 x 800 GB disks called tierPool1. Only two VDs exist in this pool, one with two-way mirroring called 2wayVD1 and one with three-way mirroring called 3wayVD1.

2wayVD1 HDD tier was 42.7 TiB, which uses 85.5 TiB of the HDD tier because of the 50 percent resiliency overhead for two-way mirroring. The SSD tier was 2 TiB in size, which uses 4 TiB of SSD tier because of resiliency overhead.

3wayVD2 HDD tier was 27.9 TiB, which uses 55.8 TiB of the HDD tier because of the 66 percent resiliency overhead from three-way mirroring. The SSD tier was 1.2 TiB, which uses 2.4 TiB of SSD tier because of resiliency overhead.

After both VDs are created, there is 33.42 TiB of disk space remaining in the HDD tier and 2.3 TiB of disk space remaining in the SSD tier.

Run the following PowerShell commands when creating a new SSD and HDD storage tier (configured for each pool).

New-StorageTier -StoragePoolFriendlyName <poolName> -FriendlyName <ssdTierName>
                                    -MediaType SSD
                                 

New-StorageTier -StoragePoolFriendlyName <poolName> -FriendlyName <hddTierName>
                                    -MediaType HDD
                                 

For example,

New-StorageTier -StoragePoolFriendlyName “tierPool1”
                                    -FriendlyName“tierPool1_SSD” –MediaType SSDNew-StorageTier 
                                    -StoragePoolFriendlyName “tierPool1” -FriendlyName“tierPool1_HDD” –MediaType HDD
                                 

Storage tiers are sized for each VD when the VD is created. You can size the SSD and HDD tiers in the GUI during VD creation or by using PowerShell.

Run the following PowerShell command for creating a VD by using existing storage tiers.

New-VirtualDisk -FriendlyName <vdName> -StoragePoolFriendlyName <poolName> 
                                    -ProvisioningType Fixed -ResiliencySettingName <Simple| Mirror| Parity> 
                                    -PhysicalDiskRedundancy <1|2> -StorageTiers <ssdTierObject, hddTierObject> 
                                    -StorageTierSizes <ssdTierSize , hddTierSize>
                                 

For example, a new VD is created called 2wayVD1 in the storage pool tierPool1. This VD is configured as a two-way mirror. The SSD and HDD tiers for this pool were created in the earlier example. Because the StorageTiers attribute requires objects as its input, the output of the Get-StorageTier PowerShell command is assigned to the $ssd_tier and $hdd_tier variables, and then used when creating the VD. The StorageTierSizes attribute is set to the size of each tier for which the VD uses the tier disk space.

$ssd_tier = Get-StorageTier -FriendlyName tierPool1_SSD

$hdd_tier = Get-StorageTier -FriendlyName tierPool1_HDD

New-VirtualDisk -FriendlyName “2wayVD1” -StoragePoolFriendlyName “tierPool1” 
                                    -ProvisioningType Fixed -ResiliencySettingName Mirror -PhysicalDiskRedundancy 1 
                                    –StorageTiers $ssd_tier, $hdd_tier –StorageTierSizes 2TB, 42.7TB