vRanger 7.8 - Integration Guide for NetVault SmartDisk

Defining a NetVault SmartDisk Storage Pool strategy

The fourth step in defining your NetVault SmartDisk Deployment Strategy is defining your strategy for the NetVault SmartDisk Storage Pools.

Understanding space allocation for NetVault SmartDisk Storage Pools

Before choosing a strategy for your NetVault SmartDisk Storage Pools, consider the following regarding how NetVault SmartDisk allocates space in the NetVault SmartDisk Storage Pools:

•	You can add an unlimited number of Storage Pools to NetVault SmartDisk.

•	You can add an unlimited number of volumes to each NetVault SmartDisk Storage Pool.

•	Each NetVault SmartDisk Storage Pool is associated with roles that it can perform.

•	When configuring a NetVault SmartDisk Storage Pool, you can identify it as a favorite for specific roles (favour), and you can indicate that it should never be used for specific roles (deny).

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There is no quota specified per-volume of the absolute amount of space NetVault SmartDisk can use; that is, you cannot say “use exactly 100 GB.” However, you can specify an amount of physical disk-storage that you want to set aside that NetVault SmartDisk cannot use. This option simplifies the NetVault SmartDisk internal space-allocation policies so that Staging Store and Chunk Store processes can efficiently share volumes. Each role independently implements and honors the configured thresholds, which allows efficient parallel-processing without a requiring a single, centralized space allocator.

•	Using the volume-size parameter, you can set aside a portion of the volume so that it cannot be used for NetVault SmartDisk. After the volume is full with NetVault SmartDisk or non-NetVault SmartDisk data, NetVault SmartDisk does not store anything else on the volume until space is made available.

•	NetVault SmartDisk uses storage space in each volume up to a threshold amount that includes space directly set aside using the volume-size parameter, and the Last Resort Threshold (LRT) amount set by NetVault SmartDisk internally.

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NetVault SmartDisk first uses a volume for its intended role, for example, Chunk Store or Staging Store, but it also uses it for other purposes if necessary. Even if you supply a threshold, NetVault SmartDisk implements an LRT that stops NetVault SmartDisk from using a volume after there is less than a certain amount of space available and thus prevents the disk from becoming full. The LRT is calculated to include both a fixed amount of space (1 GB) and the space that would be required to make Garbage Collection possible, that is, the gc_reserve_bytes parameter. This process means that the figure varies in size depending on the amount of data held in the Chunk Store; typically, you can expect the gc_reserve_bytes parameter to be at least 1.7 GB.

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If the LRT is large enough, NetVault SmartDisk properly allocates space when multiple Staging Store and Chunk Store processes are both writing to a volume that becomes too full. NetVault SmartDisk maintains an overall idea of how much space is used both by the Staging Store and the Chunk Store. This allows it to enforce the licensed amount of capacity and to enforce the LRT and the volume-size limits.

•	User thresholds and the NetVault SmartDisk LRT do not affect licensing. Licensing measures the amount of data accepted for protection by the NetVault SmartDisk Instance, regardless of whether the data has been deduplicated.

The following figure shows a graphical example of how space is organized in NetVault SmartDisk. This figure assumes that all volumes are mapped to one file system. Also, the space reserved for LRT is reserved on a per-volume basis; if your configuration uses multiple volumes, more LRT space might be allocated.

Figure 1. Space allocation for NetVault SmartDisk

Understanding the optimal performance strategy

Consider the following guidelines when assigning NetVault SmartDisk Storage Pool Roles:

•	Content Index: Should be small and reside in a Storage Pool made of fault-tolerant disks with good random-access performance.

•	Staging Store: Should reside in a Storage Pool made of fault-tolerant disks with good streaming performance.

•	Chunk Index: Should reside in a Storage Pool made of fault-tolerant disks with good random-access performance.

•	Chunk Store: Should reside in a Storage Pool made of fault-tolerant disks.

If the goal is optimal performance, using additional disks to increase Input/Output Operations per Second (IOPS) and aggregate disk bandwidth improves NetVault SmartDisk performance more than using additional memory.

For example, if you are using a single RAID array, consider configuring four separate RAID 1 volumes, one for each Storage Pool Role. This configuration separates the IO workload for each volume across independent RAID volumes. You can tune performance further by restricting the number of independent disk operations — reads, writes, and deletes — allowed per volume to two operations, which avoids disk thrashing. In addition, configure the RAID array to support more bandwidth in and out of Staging Store.

This strategy is appropriate for NetVault SmartDisk Instances where staging, deduplication, and restores might occur simultaneously.

 

NOTE: RAID recommendations also apply to Storage Area Network (SAN) and Network Attached Storage (NAS).

On Windows® platforms, you can disable the New Technology File System (NTFS) Last Access Update feature, which can reduce disk accesses and increase performance. For instructions on disabling this feature, see the documentation for your specific operating system.

Optimizing performance while protecting against data loss during power failures

Although enabling disk-write caches improves NetVault SmartDisk performance, power failures that occur before modified disk-cache contents have been written to non-volatile magnetic storage can potentially cause data loss in NetVault SmartDisk. Because of this risk, it is critical that you understand how your underlying disk technology caches writes to disk. You can turn off disk-write caching, but due to the improvement in performance that write-caching offers, it is increasingly used despite the risk, and the risk is mitigated by using additional technology. A common mitigation technique is ensuring that power does not go off. In high-end server environments, with their uninterruptible power supplies (UPSs) and redundant power supplies, having unfilled cached writes is less of an issue.

Also, drives that employ write-caching have a write-flush feature that instructs the drive to send pending writes from the cache to the disk immediately. This command is sent before UPS batteries run out — if the system detects a power interruption — or just before the system is shut down for any other reason.

Finally, most disk array systems use non-volatile random access memory (NVRAM) to protect data written to disk if there is a power failure. Quest recommends that you review your server and storage vendor’s product documentation to understand what steps are taken to ensure that disk writes are written to non-volatile magnetic storage if there is a power failure.

 

Installing vRanger

vRanger system requirements

Before installing vRanger and NetVault SmartDisk, ensure that you read and understand the requirements and limitations of both products. The system requirements for vRanger are summarized in the following topics.

For vRanger and NetVault SmartDisk to integrate, you must use the following versions:

•	vRanger 7.6.5 or later

•	NetVault SmartDisk 11.4.5 or later

 

NOTE: The following information is a summary only. Before implementing vRanger, review the Quest vRanger Installation/Upgrade Guide.