In the context of storage performance monitoring, “DAVG” stands for “Device Average Response Time.” It is a metric that indicates the average time taken by the storage device to respond to I/O requests from the hosts. The DAVG value is a critical performance metric that helps administrators assess the storage system’s responsiveness and identify potential bottlenecks.

DAVG in SAN (Storage Area Network): In a SAN environment, DAVG represents the average response time of the underlying storage arrays or disks. It reflects the time taken by the SAN storage to process I/O operations, including reads and writes, for the connected servers or hosts. DAVG is typically measured in milliseconds (ms) and is used to monitor the storage system’s performance, ensure smooth operations, and identify performance issues.

DAVG in NAS (Network Attached Storage): In a NAS environment, the DAVG metric may not directly apply, as NAS devices typically use file-level protocols such as NFS (Network File System) or SMB (Server Message Block) to share files over the network. Instead of measuring the response time of underlying storage devices, NAS monitoring often focuses on other metrics such as CPU utilization, network throughput, and file access latency.

Difference between DAVG in SAN and NAS: The main difference between DAVG in SAN and NAS lies in what the metric represents and how it is measured:

1. Meaning:
   • In SAN, DAVG represents the average response time of the storage devices (arrays/disks).
   • In NAS, DAVG may not directly apply, as it is not typically used to measure the response time of storage devices. NAS monitoring focuses on other performance metrics more specific to file-based operations.
2. Measurement:
   • In SAN, DAVG is measured at the storage device level, reflecting the time taken for I/O operations at the storage array or disk level.
   • In NAS, the concept of DAVG at the storage device level may not be applicable due to the file-level nature of NAS protocols. Instead, NAS monitoring may utilize other metrics to assess performance.
3. Protocol:
   • SAN utilizes block-level protocols like Fibre Channel (FC) or iSCSI, which operate at the block level, making DAVG relevant as a storage performance metric.
   • NAS utilizes file-level protocols like NFS or SMB, which operate at the file level, leading to different performance monitoring requirements.

It’s important to note that while DAVG is widely used in SAN environments, NAS environments may have different performance metrics and monitoring requirements. When monitoring storage performance in either SAN or NAS, administrators should consider relevant metrics for the specific storage system and application workload to ensure optimal performance and identify potential issues promptly.

Example using PowerCLI (VMware vSphere):

# Load VMware PowerCLI module
Import-Module VMware.PowerCLI

# Set vCenter Server connection details
$vcServer = "vcenter.example.com"
$vcUsername = "administrator@vsphere.local"
$vcPassword = "your_vcenter_password"

# Connect to vCenter Server
Connect-VIServer -Server $vcServer -User $vcUsername -Password $vcPassword

# Get ESXi hosts
$esxiHosts = Get-VMHost

foreach ($esxiHost in $esxiHosts) {
    # Get storage devices (datastores) on the ESXi host
    $datastores = Get-Datastore -VMHost $esxiHost

    foreach ($datastore in $datastores) {
        # Check DAVG for each datastore
        $davg = Get-Stat -Entity $datastore -Stat "device.avg.totalLatency" -Realtime -MaxSamples 1 | Select-Object -ExpandProperty Value

        Write-Host "DAVG for datastore $($datastore.Name) on host $($esxiHost.Name): $davg ms" -ForegroundColor Yellow
    }
}

# Disconnect from vCenter Server
Disconnect-VIServer -Server $vcServer -Confirm:$false

Example using NAS Monitoring Software: For NAS monitoring, you may use vendor-specific management software or third-party monitoring tools that provide detailed performance metrics for your NAS devices.

For example, suppose you are using a NAS device from a specific vendor (e.g., Tintri,NetApp, Dell EMC Isilon, etc.). In that case, you can use their management software to check performance metrics, including DAVG, related to file access and response times.

Keep in mind that the exact process and tools for monitoring DAVG in NAS environments may vary depending on the NAS device and its management capabilities. Consult the documentation provided by the NAS vendor for specific instructions on monitoring performance metrics, including DAVG.

To validate DAVG (Device Average Response Time) using esxtop for both NAS (Network Attached Storage) and SAN (Storage Area Network) in VMware vSphere, you can use the esxtop utility on an ESXi host. esxtop provides real-time performance monitoring of various ESXi host components, including storage devices. Here’s how to check DAVG in both NAS and SAN environments using esxtop with examples:

1. DAVG Check in SAN:

Example:

1. SSH to an ESXi host using an SSH client (e.g., PuTTY).
2. Run the esxtop command with the following options to view storage-related metrics:

esxtop -b -d 1 -n 1000 -a 'GAVG/DGAVG/DAVG'

• -b: Batch mode to run esxtop non-interactively.
• -d 1: Specifies the refresh interval (1 second).
• -n 1000: Specifies the number of samples to capture (1000 in this example).
• -a: Display all storage-related statistics: GAVG (Guest Average Response Time), DGAVG (Device Guest Average Response Time), and DAVG (Device Average Response Time).

2. DAVG Check in NAS:

In a NAS environment, the esxtop utility does not directly display DAVG values since NAS devices use file-level protocols for data access (e.g., NFS or SMB). Instead, monitoring in a NAS environment typically focuses on other storage metrics.

Example:

1. Follow the same steps as in the SAN example to SSH to an ESXi host and run esxtop.
2. To view file-level storage-related metrics, you can use the following esxtop options:

esxtop -b -d 1 -n 1000 -a 'CMDS/s,CMDS/s DAVG'

• -b: Batch mode to run esxtop non-interactively.
• -d 1: Specifies the refresh interval (1 second).
• -n 1000: Specifies the number of samples to capture (1000 in this example).
• -a: Display all storage-related statistics, including command rate (CMDS/s) and device average response time (DAVG).

Keep in mind that DAVG is typically more relevant in SAN environments where block-level storage is used. In NAS environments, other metrics like file access latency, IOPS, and network throughput may provide more meaningful insights into the storage performance.

Remember to analyze the esxtop output over a sufficient duration to identify trends and variations in storage performance, as real-time metrics may fluctuate. Also, make sure to consult your NAS or SAN vendor’s documentation for specific performance monitoring recommendations and metrics relevant to your storage infrastructure.