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Windows Storage Spaces automates flash usage


Microsoft’s approach to providing flash caching for virtual machines (VMs) isbased on Windows Storage Spaces rather than Hyper-V. Of course, Hyper-V is a Windows Server role and is able to fully take advantage of most Windows Storage Spaces features.

In Windows Server 2012 R2, Microsoft introduced native tiered storage with Windows Storage Spaces. The feature allows an administrator to carve up the available physical storage into storage pools. A storage pool can containsolid-state drives (SSDs), hard disk drives (HDDs) or a mixture of the two. In most cases, the Windows OS can automatically differentiate between the two storage types. In situations in which SSDs aren’t recognized as such, it’s possible to use PowerShell to manually differentiate between SSDs and HDDs.

The primary job of a Windows storage pool is to provide raw storage capacity for use by one or more virtual hard disks. Virtual disks can be created through Server Manager and can be treated as local storage or as storage for a Hyper-V VM. Many real-world deployments use a nested approach in which a virtual disk is built on top of a storage pool. That virtual disk is treated as local storage for the host OS, and the virtual hard disks used by Hyper-V VMs reside within that virtual disk.

If a virtual disk is created on top of a storage pool, the Virtual Disk Wizard checks for the presence of SSDs. If SSDs are present, the new Virtual Disk Wizard may display a checkbox the user can select to enable tiered storage. Whether or not this checkbox is displayed depends on the existence of a sufficient number of SSDs to accommodate the storage layout of the virtual disk. For example, a virtual disk that uses a mirrored layout requires two physical disks. If storage tiering is used, then two SSDs will be needed.

When a virtual disk is built using a storage tier, two things happen.

  1. The Windows OS keeps track of the storage blocks that are read most frequently. These storage blocks (which Microsoft refers to as hot blocks) are automatically moved to the high-speed storage tier. The idea is that the most frequently accessed data receives the best possible performance. It’s also possible to manually pin files to the high-speed tier, so they will always reside on high-speed storage.
  2. Windows creates a 1 GB write cache (assuming the high-speed tier is a large enough). The write cache is designed to smooth write operations. The OS can write data initially to the high-speed tier, and then move the data to a standard tier during periods of low I/O demand.

It’s possible to configure a Hyper-V VM to make direct use of a virtual hard disk that was created on top of a Windows storage pool. If Hyper-V virtual hard disks exist inside of a storage pool virtual hard disk, the Hyper-V virtual disks still receive the benefit of the underlying capabilities. It’s worth noting that Hyper-V disks will have to share the I/O bandwidth and high-speed cache of the Windows disks if multiple Hyper-V virtual hard disks reside within a single Windows virtual hard disk.

Source: Associated Press


One comment on “Windows Storage Spaces automates flash usage

  1. StellarPhoenixS
    December 22, 2014

    Reblogged this on Stellar Phoenix Solutions.

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