client, in the Storage Spaces Control Panel applet.
PERFORMANCE AND STORAGE SPACES
One concern I always had when using software RAID prior to Windows Server
2012 was performance. Any parity calculation had to use the processor, which
used up processor cycles and typically was not optimal compared to a hardware
RAID solution. This is still a concern with Storage Spaces.
Fundamentally, Storage Spaces is a software-implemented storage solution.
When using any kind of parity virtual disk, it is the operating system, specifically
the processor, that has to calculate the parity information. Using a parity
resiliency will utilize additional processor resources. In my experience, parity
utilizes only a single processor core and therefore can quickly become a
bottleneck if you are performing many disk writes, making it unsuitable for some
workloads. Therefore, my advice is as follows:
Use mirroring for workloads requiring high performance.
Use parity for archival and media-streaming purposes that don’t require
performance-critical write operations.Windows Server 2012 R2 Storage Space Changes
Windows Server 2012 R2 Storage Spaces has several improvements. One is the
capability to have dual-parity spaces, which allows up to two copies of parity
information instead of one. That provides additional resiliency (dual parity needs to be
configured using PowerShell and is not exposed in Server Manager), support for parity
spaces in cluster scenarios, and much faster rebuild in the event of a failure. The
missing information is rebuilt to many disks in the storage pool instead of rebuilding
everything to a single disk, which would limit the speed of resolution to the IOPS
possible by a single disk.
There was a bigger change in Windows Server 2012 R2 Storage Spaces that can open
up new levels of performance: a differentiation between traditional spinning hard disk
drives (HDDs) and solid-state drives (SSDs). In a Windows Server 2012 R2 storage
space, you can create different tiers of storage, an HDD tier and an SSD tier. The
Storage Spaces technology moves the most-used blocks of a file from the HDD tier
into the SSD tier, giving the highest levels of performance. Additionally, the SSD tier
can be leveraged for a write-back cache. As writes occur, they are written into the SSD
tier initially, which is very fast, and then lazily written to the HDD tier for long-term
storage. This tiering model is shown in Figure 4.4.