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New for Storage Spaces in Windows Server 2012 R2

 

Technology description


Microsoft has dramatically enhanced their software-defined storage services called “Storage Spaces” in the Windows Server 2012 R2 release, dubbed the Cloud OS.

Windows Server 2012 R2 (WS2012R2) enables cost-effective, highly available, scalable, and flexible storage solutions for business-critical virtual or physical deployments. Storage Spaces delivers sophisticated storage virtualization capabilities that empower customers to use certified storage hardware for scalable multi-node deployments as well as Cluster-in-a-Box dual-node shared storage deployments. It is appropriate for a wide range of customers including enterprise, remote brand office(ROBO) and cloud hosting companies using Windows Server for highly available and scalable storage that is cost-effective.

 

Storage Spaces works by spreading the stripes data and parity information across all the drives in the storage space. For more overview information, see Storage Spaces Overview.

 


 

New and changed functionality


Microsoft has improved Storage Spaces by adding several enterprise-grade advancements, most notably the ability to use SSDs for automated tiering and/or write-back caching. WS2012R2adds double parity using an algorithm to rebuild with less I/O than the standard RAID-6. Microsoft also added support JBOD enclosure awareness for certified SAS JBODs with expander, making Windows Servers aware of enclosure events and temperatures. The following table describes the changes in Storage Spaces functionality available in this release.

 

Storage Tiers


Storage tiers enable the creation of virtual disks comprised of two tiers of storage – an SSD tier for frequently accessed data, and a HDD tier for less-frequently accessed data. Storage Spaces transparently moves data at a sub-file level between the two tiers based on how frequently data is accessed.

 

What value does this add?


Storage tiers combine the best attributes of SSDs and hard disk drives (HDDs) in a Storage Space as a pool. Tiering tracks the access frequency of data chunks at a 1-Mbyte granularity to dynamically promote and demote chunks based on I/O “temperature” which means the most used (“hot”) data is moved to SSD storage, without sacrificing the ability to store large quantities of data on inexpensive HDDs. This tiering feature is a scheduled task that by default runs at 1 a.m. every day. Admins may adjust the schedule occurrence and set limits on the amount of the SSD tier that can be replaced in each scheduled adjustment.

 

Admins may also pin latency sensitive high I/O files—VDI “gold images”—to the SSD tier without having to dedicate volumes for them. The tiering traffic is only sent to disks when the queue for that disk is one or less, limiting the performance impact of a tiering operation.

 

What works differently?


The following aspects work differently with storage tiers:

  • To create a storage space with storage tiers, the storage pool must have a sufficient number of hard disks and SSDs to support the selected storage layout, and the disks must contain enough free space.
  • When creating a storage space using the New Virtual Disk Wizard or the New-VirtualDisk cmdlet you can now specify to create the virtual disk with storage tiers.
  • To create a storage space with storage tiers, the virtual disk must use fixed provisioning, and the number of columns will be identical on both tiers (a four-column, two-way mirror with storage tiers would require eight SSDs and eight HDDs).
  • Volumes created on virtual disks that use storage tiers should be the same size as the virtual disk.
  • Administrators can pin (assign) files to the standard (HDD) or faster (SSD) tier by using the Set-FileStorageTier cmdlet, ensuring that the files are always accessed from the appropriate tier.
  • There are new Windows PowerShell cmdlets for working with storage tiers. Additionally, the New-VirtualDisk cmdlet now includes the –StorageTiers and -StorageTierSizes parameters.

    •  
      •  
        • Set-FileStorageTier
        • Get-FileStorageTier
        • Clear-FileStorageTier
        • New-StorageTier
        • Get-StorageTier
        • Set-StorageTier
        • Resize-StorageTier
        • Remove-StorageTier
        • Get-StorageTierSupportedSize

Detailed instructions on using storage tiers: Step-by-step for Storage Spaces Tiering in Windows Server 2012 R2.

 

 

Write-back cache


The write-back caching feature creates a separate write-back cache that is tolerant of power failures and buffers short write bursts from available SSDs in the Storage Spaces pool before later writing them to HDDs.This write-back cache is intended to be stored on an SSD that’s shared in an external certified SAS JBOD to make the cache persistent across server failures in a Windows Server, Hyper-V and clusters using cluster shared volumes (CSV).

 

What value does this add?


Small random writes often dominate common enterprise workloads and can impact the performance of other data transfers that are taking place. By using SSDs (which excel at random access) for a write-back cache, Storage Spaces can reduce the latency of the random writes and also greatly reduce any impact on the performance of other data transfers.

What works differently?


The write-back cache is transparent to administrators and users and is created on all new virtual disks as long as there is a sufficient number of SSDs in the storage pool, as determined by the resiliency type of the associated storage space:

  • Simple spaces require one SSD
  • Two-way mirror spaces and single-parity spaces require two SSDs
  • Three-way mirror spaces and dual parity spaces require three SSDs

 

The write-back cache works with all types of storage spaces, including storage spaces with storage tiers.

 

Newly created storage spaces automatically use a 1 GB write-back cache by default, as long as the storage pool contains enough physical disks with MediaType set to SSD or Usage set to Journal to support the specified resiliency setting. If there aren’t enough SSD or journal disks, the write-back cache size is set to 0 except for parity spaces, when it’s set to 32 MB.

 

 

Dual Parity support for failover clusters


Windows Server 2012 R2 Storage Spaces supports single/dual parity on failover clusters, which can detect and recover from one/two simultaneous disk. When a fault occurs, the disks can be rebuilt quickly using spare storage capacity to minimize the impact on storage performance during a lengthy disk-rebuild process.

 

What value does this add?


Workloads that require greater capacity utilization, rather than mirror spaces, can now use parity spaces with one or two copies of parity information—think RAID5/RAID6—to maximize capacity and resiliency while still offering the ability to fail over to another cluster node.

 

What works differently?


The parity storage layout is an option when creating virtual disks in Server Manager or with the New-Virtual Disk cmdlet.


 

JBOD enclosure awareness


For deployments that require an added level of fault tolerance, Storage Spaces supports associating each copy of data with a particular JBOD enclosure. This capability is known as enclosure awareness, which means if one enclosure fails or goes offline, the data remains available in one or more alternate enclosures.

 

What value does this add?


Storage Spaces enclosure awareness feature mirrors the data between two enclosures. You can also use multiple SAS adapters per enclosure per server for multipathing. You can also leverage Cluster Shared Volumes I/O redirection in the event where a server loses connectivity to the JBOD but is still connected to the network.

What works differently?


To use enclosure awareness with Storage Spaces, your environment must meet the following requirements:

  • JBOD storage enclosures must support SCSI Enclosure Services (SES).
  • Tolerant levels:
    • To tolerate one failed enclosure with two-way mirrors, you need 3 compatible storage enclosures.
    • To tolerate two failed enclosures with three-way mirrors, you need 5 compatible storage enclosures.
    • To tolerate one failed enclosures with dual parity, you need 4 compatible storage enclosures.

 

 

Storage Space Configuration

All Configurations are enclosure aware

Enclosure or JBOD Count / Failure Coverage

Two JBOD

Three JBOD

Four JBOD

2-way Mirror

1 Disk

1 Enclosure

1 Enclosure

3-way Mirror

2 disk

1 Enclosure + 1 Disk

1 Enclosure + 1 Disk

Dual Parity

2 disk

2 disk

1 Enclosure + 1 Disk

 

 

Automatically rebuild storage spaces from storage pool free space


Windows Server 2012 R2 introduces a parallelized repair process, to automatically rebuild storage spaces from storage pool free space instead of using hot spares. WS2012R2 uses the remaining healthy disks to move around the data and take responsibility for the slabs of data that were stored on the failed disk.

 

What value does this add?


Rebuild times are accelerated because multiple disks in the pool can accept the data that was stored on the failed disk instead of waiting for a single hot spare to write all of the data. The recommendation is that instead of using hot spares, you instead use the disks that are spare but active capacity in the storage space, which can be available via the parallelized repair process. This will both offer more IOPS to normal production storage activity and leave your business less vulnerable during a repair process.

What works differently?


When a disk fails, instead of writing a copy of the data that was on the failed disk to a single hot spare, the data is copied to multiple drives in the pool such that the previous level of resiliency is achieved. From an admin perspective, you no longer need to allocate disks as hot spares in the storage pool, such as when adding disks to a storage pool.

 

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