Users Guide

Add-PhysicalDisk -StoragePoolFriendlyName "MyPool1" -PhysicalDisks $pd -Usage
Journal
Adding disk space to a storage pool
When planning to add physical disk space to existing storage pools and VDs there are several
considerations to be made before adding the additional physical disks or storage enclosures.
When adding a new storage enclosure to the SOFS cluster or just new physical disks to an existing
storage enclosure follow these guidelines:
• For an up-to-date list of validated storage enclosures and physical disks to confirm that the new
configuration is supported, see the Dell Storage with Microsoft Storage Spaces Support Matrix.
• For ensuring that you are following the proper cabling guidance, if adding a new storage enclosure,
see the Dell Storage with Microsoft Storage Spaces Cabling Guide.
After verifying all newly added disks are available to the cluster, you can now create new or expand an
existing storage pool or VD. Dell recommends when expanding a storage pool to add physical disks in a
quantity equal to the column count multiplied by the number of data copies plus any additional disks
required for automatic rebuilds. For example, for a Two-way mirror VD, if the column count is four, you
would add a minimum of eight disks to the pool to expand the VD.
To find out the number of columns used by a specific VD, run the PowerShell command.
Get-VirtualDisk –FriendlyName <vdName> | FL NumberOfColumns
The reasoning for the recommendation is to safeguard against expansion of VDs, which are already very
low on usable disk space. In order for a write to a VD to be successful, all data must be striped across the
number of disks indicated by the column count. If you add fewer disks, there may be new free disk space
now on the VD, there is still not enough disks available for a full stripe to be written.
For example,
A 2x3 configuration with three Dell Storage MD1400 storage enclosures each with eight HDDs and four
SSDs. For example, all 24 HDDs and 12 SSDs are added to one storage pool called MyPool1. One VD is
created using storage tiers in the pool — 2wayVD1, with Two-way mirroring and a column count of 5.
The plan is to add an extra Dell Storage MD1400 enclosure with eight new HDDs and four new SSDs.
For this example, 2wayVD1 had data added so that almost no usable disk space is remaining in the HDD
tier. In an effort to add new disk space, all eight of the new HDDs are added to MyPool1. 2wayVD1 has a
column count of five, which means a total of 10 disks are required for a full stripe, one stripe across five
disks for first data copy and one stripe across another five disks for the second data copy. However,
because only eight HDDs were added to the pool, after the original disks in the pool are completely out
of disk space there will now only be eight disks, and not the 10 required to write to 2wayVD1.
There is one more factor to consider when adding physical disks or storage enclosures with the intent of
expanding existing VDs which were created with enclosure awareness. Enclosure awareness spreads the
data copies of VDs across three or more storage enclosures. However, when adding new physical disks
or storage enclosures, depending on the existing VD layout, VDs created on the newly added storage disk
space may not be enclosure aware. This occurs if there is not sufficient free disk space or there are not
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