Storage Spaces were first introduced in Windows 2012. Windows Server 2012 R2 provides the following enhancements to Storage Spaces:
• Tiered Storage Spaces. Tiered Storage Spaces enable you to use a combination of disks in a Storage Space, for example very fast, but small-capacity hard disks (such as solid state driver [SSDs]) alongside slower, but large-capacity hard disks. When you use this combination of disks, Storage Spaces automatically moves frequently-accessed data to the faster hard disks and moves less frequently- accessed data to the slower disks. By default, Storage Spaces moves data once day at 01:00 A.M. You can also configure where files are stored. The advantage is that if you have files that are frequently accessed, you can pin them to the faster disk. The goal of tiering is to balance capacity against performance. Windows Server 2012 R2 recognizes only two levels of disk tiers, SSD and non-SSD. • Write-back caching. The purpose of write-back caching is to optimize writing data to the disks in a
Storage Space. Write-back caching typically works with Tiered Storage Spaces. If the server that is running the Storage Space detects a peak in disk-writing activity, it automatically starts writing data to the faster disks. By default, write-back caching is enabled but also limited to 1 GB of data.
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3-20 Managing Storage in Windows Server 2012
Storage Spaces Features
To configure Storage Spaces as per your requirements, you must consider the features described in the following table before you implement virtual disks.Feature Description
Storage layout This defines the number of disks from the storage pool that are allocated. Valid options are:
• Simple. A simple space has data striping but no redundancy. In data striping, logically sequential data is segmented across all disks in a way that enables different physical storage drives to access these sequential
segments. Striping makes it possible to access multiple segments of data at the same time so this option can improve performance. To enable data striping, you must deploy at least two disks. You can also use a single disk when implementing storage space using the simple storage layout. The simple storage layout does not provide any redundancy, so if one disk in the storage pool fails, all data will be lost.
• Two-way and three-way mirrors. Mirror spaces maintain two or three copies of the data they host (two data copies for two-way mirrors and three data copies for three-way mirrors). Duplication occurs with every write to ensure that all data copies are always current. Mirror spaces also stripe the data across multiple physical drives. To implement mirroring, you must deploy at least two or three physical disks. Mirroring provides protection against the loss of one or more disks, so use mirroring when you are storing important data. The disadvantage of using mirroring is that the data is duplicated on two or three disks, so disk usage is not efficient.
• Parity. A parity space resembles a simple space in that data is written across multiple disks. However with the parity storage layout, parity information is also written across the disks. The parity information can be used to calculate data if a disk is lost. Parity enables Storage Spaces to continue to service read and write requests even when a drive has failed. The parity information is always rotated across available disks to enable IO optimization. A storage space requires a minimum of three physical drives for parity spaces. Parity spaces have increased resiliency through journaling. The parity storage layout provides redundancy, but is more efficient in utilizing disk space than mirroring.
Disk sector size A storage pool's sector size is set the moment it is created. If the list of drives being used contains only 512 and 512e drives, the pool is defaulted to 512e. A 512 disk uses 512-byte sectors. A 512e drive is a hard disk with 4,096-byte sectors that emulates 512-byte sectors. If the list contains at least one 4-KB drive, the pool sector size is defaulted to 4 KB. Optionally, an administrator can explicitly define the sector size that all contained spaces in the pool will inherit. After an administrator defines this, Windows will only enable addition of drives that have a compliant sector size, that is: 512 or 512e for a 512e storage pool, and 512, 512e, or 4 KB for a 4-KB pool.
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Upgrading Your Skills to MCSA Windows Server® 2012 3-21
Feature Description
Cluster disk
requirement computer failure. For a pool to support failover, clustering all assigned drives Failover clustering prevents interruption to workloads or data if there is a must support SAS.
Drive allocation This defines how the drive is allocated to the pool. Options are:
• Data-store. This is the default allocation when any drive is added to a pool. Storage spaces can automatically select available capacity on data-store drives for both storage space creation and just-in-time allocation.
• Manual. Administrators can choose to specify manual as the usage type for drives added to a pool. A manual drive is not automatically used as part of a storage space unless it is specifically selected at the creation of that storage space. This usage property lets administrators specify particular types of drives for use only by certain storage spaces.
• Hot-Spare. Drives added as “Hot-Spares” to a pool are reserve drives that are not used in the creation of a storage space. If a failure occurs on a drive that is hosting columns of a storage space, a reserve drive is called on to replace the failed drive.
Provisioning
schemes •You can provision a virtual disk by using two schemes: Thin provisioning space. Thin provisioning is a mechanism that enables storage to be easily allocated on a just-enough and just-in-time basis. Storage capacity in the pool is organized into provisioning slabs that are not allocated until the point in time when datasets grow to actually require the storage. Instead of the traditional fixed storage allocation method, in which large pools of storage capacity are allocated but may remain unused, thin provisioning optimizes use of available storage. Organizations may also be able to reduce operating costs, such as electricity and floor space that are associated with keeping unused drives spinning.
• Fixed provisioning space. In Storage Spaces, fixed provisioned spaces also use the flexible provisioning slabs. The difference is that the storage capacity is allocated up front, at the time that the space is created.
Note: Storage spaces allows for the creation of both thin and fixed provisioning virtual disks within the same storage pool. Having both provisioned types in the same storage pool is convenient, especially when they are related to the same workload. For example, you can choose to have a thin provisioning space to host a shared folder containing user files, and a fixed provisioning space to host a database that requires high disk I/O.