This guide provides best practices for customers using Dell Unity All-Flash storage systems in a VMware vSphere environment. This paper focuses on optimizing system performance and maximizing the usability of Dell Unity automated storage features when used with VMware vSphere. For general best practices on using Dell Unity systems, see the Dell Unity: Best Practices Guide.

These guidelines are intended to cover most use cases. They are strongly recommended by Dell Technologies but are not strictly required.

This paper was developed using the Dell Unity XT 480F All-Flash array, but is also applicable when using the 380F, 680F, or 880F Dell Unity XT All-Flash arrays.

If you have questions about the applicability of these guidelines in your environment, contact your Dell Technologies representative to discuss the appropriateness of the recommendation.

Dell Technologies and the authors of this document welcome your feedback on this document. Contact the Dell Technologies team by email.

Author: David Glynn

Contributors: Jason Gates

As of Dell UnityOS 5.4, Dell Unity supports two types of storage pools on all-flash storage systems: traditional pools and dynamic pools. Traditional pools apply RAID protection to discrete groups of drives within the storage pool. Dynamic pools apply RAID to groups of drive extents from drives within the pool and allow for greater flexibility in managing and expanding the pool. Prior to UnityOS 5.2, dynamic pools could only be configured from all-flash drives; With UnityOS 5.2 and later include support for Dynamic Pools on Hybrid systems. All newly created pools including multi-tiered pools on the Hybrid system will be created as Dynamic Pools by default.

In general, it is recommended to use a small number of storage pools within Dell Unity storage to reduce complexity and increase flexibility. However, it may be appropriate to configure additional storage pools in the following cases:

• Separate workloads with different I/O profiles
• Dedicate resources to meet specific performance goals
• Separate resources for multi-tenancy
• Create smaller failure domains

Storage pool capacity

Storage pool capacity is used for multiple purposes:

• To store all data written into storage objects — LUNs, file systems, datastores, and VMware vSphere Virtual Volumes (vVols) — in that pool
• To store data that is needed for snapshots of storage objects in the pool
• To track changes to replicated storage objects in that pool

Storage pools must maintain free capacity to operate properly. By default, Dell Unity systems will raise an alert if a storage pool has less than 30% free capacity and will begin to automatically invalidate snapshots and replication sessions if the storage pool has less than 5% free capacity. Dell Technologies recommends that a storage pool always has at least 10% free capacity.

All-flash pool

All-flash pools provide the highest level of performance in Dell Unity arrays. Use an all-flash pool when the application requires the highest storage performance at the lowest response time.

• Dell Technologies FAST Cache and FAST VP are not applicable to all-flash pools.
• Data Reduction is supported on an all-flash pool.
• Snapshots and replication operate most efficiently in all-flash pools.
• Dell Technologies recommends using only a single drive size and a single RAID width within an all-flash pool.

For example, for an all-flash pool, use only 1.6 TB SAS flash 3 drives and configure them all with RAID 5 8+1 configuration.

Hybrid pool

Hybrid pools are configurable on Dell Unity Hybrid arrays.

This section describes some of the native features available on the Dell Unity platform. Additional information on each of these features can be found in the Dell Unity: Best Practices Guide. Features not applicable to the all-flash array models covered by this paper are noted.

FAST VP accelerates performance of a specific storage pool by automatically moving data within that pool to the appropriate drive technology based on data access patterns. FAST VP is only applicable to hybrid pools within a Dell Unity Hybrid flash system.

FAST Cache is a single global resource that can improve performance of one or more hybrid pools within a Dell Unity Hybrid flash system. FAST Cache can only be created with SAS flash 2 drives and is only applicable to hybrid.

To help reduce the Total Cost of Ownership and increase the efficiency of a Dell Unity storage system, Dell Unity Compression was added in Dell UnityOS version 4.1 for Thin Block storage resources. Thin File storage resource support was added in Dell UnityOS version 4.2. In Dell UnityOS version 4.3, the Dell Unity Data Reduction feature replaces compression and provides more space savings logic to the system with the addition of zero block detection and deduplication.

In Dell UnityOS version 4.5, Data Reduction includes an optional feature called Advanced Deduplication, which expands the deduplication capabilities of the Data Reduction algorithm. With data reduction, the amount of space required to store a dataset for data reduction enabled storage resources is reduced when savings are achieved. This space savings reduces the amount of physical storage required to store a dataset, which can lead to cost savings.

Data reduction savings are not only achieved on the storage resource it is enabled on, but space savings are also realized on Snapshots and Thin Clones of those resources as well. Snapshots and Thin Clones inherit the data reduction setting of the source storage resource, which helps to increase the space savings that they can provide.

Data at Rest Encryption (D@RE) is controller-based encryption that does not impact system performance. Dell Technologies recommends ordering Dell Unity systems as encryption-enabled, if appropriate for your environment.

Note: Encryption can only be enabled at the time of system installation with the appropriate license.

If encryption is enabled, Dell Technologies recommends making external backups of the encryption keys after system installation as well as immediately following any change in the system’s drive configuration (such as creating or expanding a storage pool, adding new drives, or replacing a faulted drive). Additional information regarding Data at Rest Encryption can be found in the Dell Unity: Data at Rest Encryption white paper.

Dell Technologies recommends setting host I/O limits on workloads that might monopolize pool resources and starve other applications of their required performance. As of UnityOS 5.5 host I/O limits are supported for both block and file resources.

For example: Limit the bandwidth available to large-block applications that may increase the latency on other small-block workloads.

Additional information can be found in the Dell Unity: Unisphere Overview white paper.

This section provides configuration recommendations and storage access guidelines for integrating VMware vSphere 8.x hosts with the Dell Unity All-Flash array models.

Zoning Fibre Channel switches to connect vSphere hosts to a Dell Unity array is like most zoning processes. This section explains the fundamentals of recommended zoning.

Single initiator zoning

Each Fibre Channel zone created should contain a single initiator (host HBA port) and all applicable storage target ports. In other words, each HBA port on the host requires its own zone, containing itself and the applicable storage ports. For resiliency and availability, two fabrics should be used, each containing half of the ports on each host and half of the ports on each storage processor (SP) on the Dell Unity array.

WWN zoning

World Wide Name (WWN) zoning provides the most flexible zoning configuration since it is based on the WWN of each port, regardless of the physical port on the switch where it is connected. For single initiator zoning with WWNs, the WWN of each host port would have its own zone and would also contain the applicable storage port WWNs.

Port zoning

Port zoning refers to including physical ports on the Fibre Channel switch in each zone rather than the WWN as described above. Unless your environment requires the use of port zoning, WWN zoning is the recommended method.

Dell Unisphere, the graphical management interface for Dell Unity systems, can be used to present storage to all host servers. For vSphere hosts, Unisphere utilizes integration points to reduce required steps and perform several host-side functions. To take advantage of the integration point, the vSphere host, or vCenter environment must be imported into the Unisphere interface (this requires credentials for the vSphere host or the vCenter server). Once imported, the presentation of VMware VMFS, NFS, or vVol datastore storage from Unisphere results in mounted datastore(s) on the hosts. Additional information and detail can be found in the Dell Unity: Unisphere Overview and Dell Unity: Virtualization Integration white papers.

Block storage (both iSCSI and FC) presented to vSphere hosts from Dell Unity has the native Path Selection Policy (PSP) of round robin (RR) applied by default. While RR is the recommended PSP to apply to Dell Unity block storage, the default number of I/Os between switching paths is 1000. By reducing this value, all paths are more efficiently utilized. Additional information on this topic can be found in the Adjusting Round Robin IOPS limit from default 1000 to 1 article in the VMware Knowledge Base.

Internal lab testing has indicated that adjusting the RR policy to iops=1 has shown up to a 121% increase in IOPS, and up to a 32% reduction in latency for vVol and VMFS datastores. It is recommended to test this in your environment to determine if this change positively affects your workloads.

A claim rule can be created to automatically set this value on future LUNs mapped to the host. This must be performed on all hosts and requires a reboot to take effect.

esxcli storage nmp satp rule add --satp "VMW_SATP_ALUA_CX" --vendor "DGC" --psp "VMW_PSP_RR" --psp-option "iops=1" --claim-option="tpgs_on"

Dell Unity LUNs presented to vSphere hosts through iSCSI should utilize the following best practices.

Enabling jumbo frames

On the Dell Unity array (in Unisphere click Settings > Access > Ethernet), as well as on all vSphere hosts accessing its iSCSI storage, the MTU size should be set to 9000 to enable the transmission of large blocks of data, which is more efficient than the default MTU size with block-based storage. Additionally, all Ethernet switches in the iSCSI data path must support jumbo frames. Refer to the specific switch configuration guide for instructions on enabling jumbo frames.

Disable delayed ACK

In some environments, periods of high network congestion can cause iSCSI transfer latency to exceed acceptable levels. To avoid this, VMware recommends disabling delayed ACK following the steps provided in the VMware Knowledge Base article ESX/ESXi hosts might experience read or write performance issues with certain storage arrays.

LUN sizing and creation

Determining the size and number of LUNs to create and present to your vSphere environment is a complex task. This section does not provide specific recommendations for the size and number of LUNs because every environment is different, but it provides guidance for identifying the most effective configuration for your environment.

LUN size

VMware currently supports a maximum datastore size of 64 TB. However, in most circumstances, a much smaller, more manageable size is recommended to accommodate a reasonable number of virtual machines (VMs) per datastore (learn more in section 3.5.2). Since LUNs and vSphere datastores can be expanded to address future growth, the recommendation is to create LUNs and datastores with sizes in the range of 500–750 GB for most environments. This size of datastore accommodates 10–15 virtual machines with a 40 GB virtual disk and provides the additional capacity required for the various overhead files for each virtual.

Note: This sizing recommendation supports limitations on the number of virtual machines on each datastore to keep performance optimal. This recommendation does not consider high-capacity virtual machines. Virtual machines requiring a large virtual disk would require a larger LUN/datastore size and would not be exempt from these best practices.

Virtual machines per datastore

VMware currently supports a maximum of 2,048 powered-on virtual machines per VMFS datastore. However, in most circumstances and environments, a target of 15–25 virtual machines per datastore is the conservative recommendation.

By maintaining a smaller number of virtual machines per datastore, potential for I/O contention is reduced, resulting in more consistent performance across the environment. For this reason, the recommended LUN/datastore size is 1–3 TB.

Note: The virtual machines per datastore recommendation should be adjusted to support your environment. The appropriate number should be based on the I/O and capacity requirements for your specific environment.

VMFS partition alignment

Dell Unity block LUNs where VMFS datastores are created do not require alignment because VMFS automatically aligns the partition at creation time.

Guest virtual SCSI adapter

When creating a new virtual machine, vSphere automatically selects the recommended virtual SCSI controller based on the operating system being installed to the VM. The best practice is to maintain the automatically selected virtual SCSI controller under most circumstances. In some cases, changing to the VMware Paravirtual SCSI controller may result in better I/O performance as well as reduced CPU utilization on the VM. Also, configure the SCSI controller driver in the guest operating system to a large enough queue.

Thin provisioning and virtual disks

Thin provisioning of storage, from both Dell Unity storage and virtual disks created as part of a virtual machine, allows for increased space efficiency in the storage environment. Thinly provisioned storage can be configured with substantial sizes but will only occupy the storage capacity required to accommodate the actual storage needs. This ability reduces upfront storage costs in many cases and allows for a more manageable and predictable storage growth over time.

Virtual disk

When creating a virtual machine, one or more virtual disks are created as part of the virtual hardware of that virtual machine. There are three virtual disk formats to choose from:

The default virtual disk format is thick provision lazy zeroed. The best practice is to use the default virtual disk format unless specific needs dictate the use of thick provisioned eager zeroed for performance or availability needs including Microsoft Cluster Service (MSCS) and VMware Fault Tolerance (FT).

With the release of vSphere 8.0, VMware has improved the first-write process when using thin provisioned VMDKs. While VMware still recommends using Eager Zeroed Thick (EZT) virtual disks for maximum performance, this new method should decrease much of performance impact when allocating new space on new writes.

Dell Unity storage offers thin provisioning as a recommended option when creating block storage and requires thin provisioning to enable compression. Utilizing thin provisioning within VMware on virtual disks does not initially result in additional space efficiency when thin provisioning is enabled on the array. However, the ability to reclaim space from within a compatible guest OS does require thin provisioning to be used on both the storage and the virtual disks. Additional requirements for space reclamation within the guest include the following:

Virtual machines on VMFS 6 datastores

• Reclaiming space on a guest operating system is only processed when the space to reclaim is equal to 1 MB or a multiple of 1 MB.
• Supports 4Kn storage devices.

Virtual machines on VMFS 5 datastores

• Virtual machine hardware must be version 11 (ESXi 7.0) or greater.
• The advanced setting EnableBlockDelete must be set to 1.
• The guest operating system must be able to identify the virtual disk as thin. This section describes some of the native features available on the Dell Unity platform. Additional information on each of these features can be found in the Dell Unity: Best Practices Guide. Features not applicable to the all-flash array models covered by this paper are noted

When creating NFS-based storage for vSphere in a Dell Unity environment, Dell Technologies recommends creating VMware NFS datastores using the VMware-specific tools within Unisphere, rather than using general-purpose NFS file systems. VMware NFS datastores are optimized to provide better performance with vSphere.

 Additionally, creating two NAS servers (one on each SP) on the Dell Unity platform where NFS datastores are served is recommended for both availability and increased performance. Dell Technologies also recommends using the default 8K Host I/O Size for VMware NFS datastores. Only choose a different host I/O size if all applications that will be hosted in the NFS datastore primarily use the selected I/O size.

When configuring block Virtual Volume (vVol) datastores over Fibre Channel or iSCSI, protocol endpoint devices are presented to the vSphere hosts rather than disk devices. These protocol endpoint devices are used for tuning as described in section 3.3. Best practices regarding block vVol datastores mirror those of the standard block storage described previously in this paper.

When configuring file-based (NFS) vVol datastores in a Dell Unity environment, it is recommended to create at least two vVol-enabled NAS servers: one on SPA and the other on SPB. Additionally, committing two or more interfaces per SP can result in better performance, but this follows the same guidelines and limitations as NFS datastores described in Best Practices for Running VMware vSphere on Network-Attached Storage (NAS).

This section covers features or products used for data protection. It also covers how storage administrators or application administrators use or integrate application data protection features.

Dell Technologies AppSync is software that enables integrated Copy Data Management (iCDM) with Dell Technologies primary storage systems, including Dell Unity arrays.

AppSync simplifies and automates the process of creating and using snapshots of production data. By abstracting the underlying storage and replication technologies, and through application integration, AppSync empowers application owners to manage data copy needs themselves. The storage administrator, in turn, need only be concerned with initial setup and policy management, resulting in a more agile environment.

Be aware that snapshots increase the overall CPU load on the system and increase the overall drive IOPS in the storage pool. Snapshots also use pool capacity to store the older data being tracked by the snapshot, which increases the amount of capacity used in the pool until the snapshot is deleted. Consider the overhead of snapshots when planning both performance and capacity requirements for the storage pool.

Before enabling snapshots on a storage object, it is recommended to monitor the system and ensure that existing resources can meet the additional workload requirements. Refer to the Hardware Capability Guidelines section and Table 2 in the Dell Unity Best Practices Guide. Enable snapshots on a few storage objects at a time and then monitor the system to be sure it is still within the recommended operating ranges before enabling more snapshots. Additional information can be found in the Dell Unity: Snapshots and Thin Clones white paper.

Dell Technologies recommends including a flash tier in a hybrid pool where asynchronous replication will be active. This is applicable to both the source and the destination pools.

Asynchronous replication takes snapshots on the replicated storage objects to create the point-in-time copy, determining the changed data to transfer and maintaining consistency during the transfer. Consider the overhead of snapshots when planning performance and capacity requirements for a storage pool that will have replication objects.

Setting smaller recovery point objective (RPO) values on replication sessions will not make them transfer data more quickly, but smaller RPOs will result in more snapshot operations. Choosing larger RPOs, or manually synchronizing during non-production hours, may provide more predictable levels of performance. Additional information can be found in the Dell Unity: Replication Technologies white paper.

Dell Technologies recommends including a flash tier in a hybrid pool where synchronous replication will be active.

Synchronous replication transfers data to the remote system over the first Fibre Channel port on each SP. When planning to use synchronous replication, it may be appropriate to reduce the number of host connections on this port. Additional information can be found in the Dell Unity: Replication Technologies white paper.

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