FAQs about NetApp Cloud Volumes Service for Google Cloud

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Last reviewed 2022-01-24 UTC

This document answers frequently asked questions (FAQs) about NetApp Cloud Volumes Service for Google Cloud.

Application resilience FAQs

This section provides answers to frequently asked questions about application resilience in NetApp Cloud Volumes Service for Google Cloud.

How can I handle potential application disruptions due to storage service maintenance events?

Planned maintenance such as platform updates, service upgrades, and software upgrades might occur occasionally in Cloud Volumes Service. These maintenance operations are considered non-disruptive from a file protocol, NFS, or SMB perspective as long as the application can handle the I/O pauses that might occur during these events. The I/O pauses are typically short, ranging from a few seconds up to 30 seconds.

  • NFS: During maintenance, client-server file operations continue normally. I/O to a hard-mounted NFS share waits until the server starts to respond again. The NFSv4 protocol adds a lock-state recovery period of 30 seconds where no read/write operations are served. It starts after the NFSv4 server restarts. For more information on NFSv4.x lock state recovery, refer to NFSv4.x RFC, section 9.6.2.

    The CVS service type exhibits longer I/O pauses in some cases. In these cases, the recommended NFSv3 timeout is 120 seconds when using a watchdog process for high-availability configurations.

  • SMB: For SMB protocol, the session timeout is defined at the client. The default timeout for Windows clients is 60 seconds. You can read or change the session timeout by running the Get-SmbClientConfiguration/Set-SmbClientConfiguration command using the SessionTimeout parameter.

    If a timeout occurs, the SMB session is broken and needs to be re-established. Sessions with human interaction usually reconnect as soon as the user accesses the SMB share again. Applications receive an I/O error timeout and need to handle reconnects using application logic. Consult your application vendor to learn how the application handles SMB timeouts and how to use SMB in a resilient fashion.

    Some supported applications can use Continuously Available shares for automatic timeout recovery.

    Failure recovery improves with every SMB version. If possible, use the latest supported SMB version (SMB3.x).

Do I need to take special precautions for SMB-based applications?

Yes. SMB Transparent Failover is required for certain SMB-based applications. SMB Transparent Failover enables maintenance operations on SMB volumes within Cloud Volumes Service without interrupting connectivity to server applications storing and accessing data. Cloud Volumes Service supports the SMB Continuously Available shares option to make sure specific applications support SMB Transparent Failover. Using SMB Continuously Available shares is only supported for workloads on the following applications:

  • FSLogix user profile containers.

  • Microsoft SQL Server.

Linux SQL Server isn't supported.

Custom applications aren't supported with SMB Continuously Available shares.

Security FAQs

This section provides answers to frequently asked questions about the security and architecture elements of the Cloud Volumes Service for Google Cloud.

For details, including information about how data is encrypted, see the NetApp technical report TR-4918: Security overview - NetApp Cloud Volumes Service in Google Cloud.

Is the data encrypted in transit between a cloud volume and a Compute Engine instance?

Data traverses over standard Google VPC constructs between a cloud volume and a Compute Engine instance that inherit any in-transit encryption features provided by those constructs.

You can enable SMB encryption on a volume.

You can enable NFSv4.1 Kerberos encryption on a volume of the CVS-Performance service type.

How is access to the data in a cloud volume restricted to specific Compute Engine instances or users?

For NFS volumes, access to mount volumes is controlled by export policies. You can set up to five export policies per volume to control which instances (by IP addresses) have access and what kind of access (read only, read/write) they have.

For SMB volumes, a user-supplied Active Directory (AD) server is required. The AD server handles authentication and authorization to the SMB cloud volume, and you can configure it to handle granular access with NTFS ACLs.

Are there IAM controls to specify who can administer Cloud Volumes Service?

Yes. Cloud Volumes Service provides granular permissions for all objects in the Cloud Volumes Service API such as volumes, snapshots, and Active Directory. These granular permissions are fully integrated into the IAM framework. The permissions are integrated into two predefined roles: netappcloudvolumes.admin and netappcloudvolumes.viewer. You can assign these roles to users and groups per project to control administration rights for Cloud Volumes Service. For more information, see Permissions for Cloud Volumes Service.

How is access to the Cloud Volumes Service API secured?

There are two layers of security to access the Cloud Volumes Service API:

  • Authentication: The caller of the API is required to supply valid JSON web tokens. For details, see Manage API authentication. You can disable or delete service accounts to revoke the ability to make calls to the Cloud Volumes Service API.
  • Authorization: Cloud Volumes Service checks the granular permission against IAM for each operation requested on the API (when an authenticated request is received). Authentication alone is not sufficient to access the API.

For more information about how to set up a service account, obtain permissions, and call the Cloud Volumes Service API, see Cloud Volumes APIs.


This section provides answers to FAQs about the NFS elements of the Cloud Volumes Service for Google Cloud.

How does NFSv4.1 handle user identifiers?

Cloud Volumes Service enables numerical user identifiers (UIDs) for NFSv4.1 using sec=sys. That means Unix UIDs and group identifiers (GIDs) are used to identify users and groups. It also means that NFSv4.1 clients should work immediately without complex user identity management. The only exception is the root user, which functions properly as root, but gets displayed as UID= 4294967294 in the ls output. To fix this, edit the /etc/idmapd.conf configuration file in your clients to contain the following:

domain = defaultv4iddomain.com

If you're using LDAP, then use the fully qualified domain name (FQDN) for your AD domain:

domain = FQDN_of_AD_domain

Modern Linux clients are configured to support numerical IDs by default. If your client doesn’t, you can enable numerical IDs with the following command:

echo "Y" > /sys/module/nfs/parameters/nfs4_disable_idmapping

What are the Linux NFS concurrency recommendations?

NFSv3 does not have a mechanism to negotiate concurrency between the client and the server. The client and the server each defines its limit without consulting the other. For the best performance, use the maximum number of client-side sunrpc slot table entries that doesn't cause pushback on the server. When a client overwhelms the server network stack’s ability to process a workload, the server responds by decreasing the window size for the connection, which can decrease performance.

By default, modern Linux kernels define the per-connection slot table entry size (sunrpc.max_tcp_slot_table_entries) as supporting 65,536 outstanding operations, and volumes of the CVS service type enforce a limit of 128 slots for each NFS TCP connection. You do not need to use values this high. In queueing theory, Little's Law says that concurrency is the product of the operation rate and the latency. This means that the I/O rate is determined by concurrency (that is, outstanding I/O) and latency. 65,536 is orders of magnitude more than the number of slots needed for even extremely demanding workloads.

For example, a latency of 0.5 ms and a concurrency of 128 can achieve up to 256,000 IOPS. A latency of 1 ms and a concurrency of 128 can achieve up to 128,000 IOPS.


  • NFS clients with normal traffic infrequently use more than 128 slots, so you do not need to take any action for these clients.
  • If you have a few clients that need to push heavy NFS traffic (for example, databases or compute applications), limit their queues to 128 slots by setting the kernel parameter sunrpc.tcp_max_slot_table_entries to 128. The way to make the setting persist depends on the Linux distribution:

    If your application requires higher IOPS, consider using the nconnect mount option to use multiple TCP connections.

  • If you have many clients (more than 30) that need to push heavy NFS traffic—such as in compute farms for high-performance computing (HPC) or electronic design automation (EDA) workflows—consider setting sunrpc.tcp_max_slot_table_entries to 16 to improve aggregated performance. The sunrpc.tcp_max_slot_table_entries kernel parameter is only available after the sunrpc kernel module is loaded. It is loaded automatically by the nfs kernel module.


This section provides answers to FAQs about the SMB elements of the Cloud Volumes Service for Google Cloud.

Why does the cloud volumes SMB NetBIOS name not reflect the name configured for the cloud volume?

NetBIOS names have a length of 15 characters. You can specify up to 10 characters, and Cloud Volumes Service adds a suffix of a hyphen and 4 random hexadecimal digits to form the full NetBIOS name.

Example: \\myvolname becomes \\myvolname-c372

Why can't my client resolve the SMB NetBIOS name?

You can map or mount an SMB share created with Cloud Volumes Service by using its uniform naming convention (UNC) path, which the UI displays. A UNC path follows the pattern \\HOSTNAME\SHARENAME (for example, \\cvssmb-d2e6.cvsdemo.internal\quirky-youthful-hermann). The hostname is only resolvable through the AD’s built-in DNS servers. Windows hosts joined to the AD domain usually use these DNS servers. Servers not belonging to the domain might use different DNS servers (such as Cloud DNS) and cannot resolve the hostname. This is very common for Linux VMs in a Google Cloud project and for Windows clients not joined to the domain.

You can use an IP address instead. You can determine the IP address by querying the AD DNS servers:

  • Linux:

        dig @AD_SERVER_IP_ADDRESS +short cvssmb-d2e6.cvsdemo.internal
  • Windows:

        nslookup cvssmb-d2e6.cvsdemo.internal AD_SERVER_IP_ADDRESS

Alternatively, you can create a forwarding zone to your AD DNS servers so that a client using your DNS server can resolve fully qualified domain names from the UNC path. The following example demonstrates the creation of a forwarding zone with Cloud DNS:

    gcloud dns managed-zones create my-ad \
      --project=my-project \
      --description="" \
      --dns-name="cvsdemo.internal." \
      --visibility="private" \
      --networks="my-vpc" \

How can I check whether my SMB share is using SMB encryption?

When you map an SMB share, the client and server negotiate the SMB version and features, such as SMB encryption. After you enable SMB encryption for a volume, the CVS SMB server requires SMB encryption. This means that only SMB3 clients that support SMB encryption can access the volume.

To verify whether your SMB connection is using SMB encryption, map a CVS share and run the following PowerShell command:

Get-SmbConnection -servername [CVS_IP_OR_NETBIOS_NAME] | Select-Object -Property Encrypted

How can I identify Active Directory domain controllers used by the CVS and CVS-Performance service types?

Cloud Volumes Service uses Active Directory connections to configure volumes of the CVS and CVS-Performance service types. Each service type can have one AD connection for each Google Cloud region.

Microsoft recommends placing Active Directory domain controllers (DCs) close to SMB servers for good performance. For Google Cloud, place DCs in the same region where Cloud Volumes Service is used. For the CVS service type, DCs must be in the same region; otherwise, volumes of the CVS service type can’t connect to DCs. NetApp recommends having at least two DCs for each region, for service resilience.

Cloud Volumes Service uses standard DNS-based discovery to find suitable DCs. Use the following query to get the list of all DCs in your domain:

  • Windows:

    nslookup -type=srv _ldap._tcp.dc._msdcs.<domain-name> <dns-server>
  • Linux:

    dig @<dns-server> +short SRV _ldap._tcp.dc._msdcs.<domain-name>

For volumes of the CVS service type, you must limit the list to DCs installed only in a given Google Cloud region. For volumes of the CVS-Performance service type, limiting the list is recommended, but not required. When you create an Active Directory site, make sure that it contains only DCs located in the desired Google Cloud region. After you create a site, use the following command to check which DCs are contained in the list:

  • Windows:

    nslookup -type=srv _ldap._tcp.<site_name>._sites.dc._msdcs.<domain-name> <dns-server>
  • Linux:

    dig @<dns-server> +short SRV _ldap._tcp.<site_name>._sites.dc._msdcs.<domain-name>

Verify that the returned list only contains DCs that are in the desired Google Cloud region.

In your Active Directory connection configuration, enter the AD site name.

Which permissions are needed to create Active Directory machine accounts?

To add CVS machine objects to a Windows Active Directory, you need an account that either has administrative rights to the domain or has delegated permissions to create and modify machine account objects to a specified organizational unit (OU). You can grant these permissions with the Delegation of Control Wizard in Active Directory by creating a custom task that provides a user access to creation and deletion of computer objects with the following access permissions provided:

  • Read/Write
  • Create/Delete All Child Objects
  • Read/Write All Properties
  • Change/Reset Password

Creating this custom task adds a security ACL for the defined user to the organizational unit in Active Directory and minimizes the access to the Active Directory environment. When a user has been delegated, that username and password can be provided as Active Directory credentials in this window.

SMB performance FAQs

This section answers FAQs about SMB performance best practices for Cloud Volumes Service for Google Cloud.

Is SMB Multichannel enabled by default in SMB shares?

Yes, SMB Multichannel is enabled by default. All currently existing SMB volumes have the feature enabled, and all newly created volumes also have the feature enabled.

You need to reset any SMB connection established prior to the feature enablement to take advantage of the SMB Multichannel functionality. To reset, disconnect and reconnect the SMB share.

Does Cloud Volumes Service support receive-side scaling (RSS)?

With SMB Multichannel enabled, an SMB3 client establishes multiple TCP connections to the Cloud Volumes Service SMB server over a network interface card (NIC) that is single RSS capable.

Which Windows versions support SMB Multichannel?

Windows has supported SMB Multichannel since Windows 2012. For more information, see Deploy SMB Multichannel and The basics of SMB Multichannel.

Do Google Cloud virtual machines support RSS?

To see if your Google Cloud virtual machine NICs support RSS, run the command Get-SmbClientNetworkInterface from PowerShell. Then in the output, check the RSS Capable column:

Output showing RSS capability.

Does Cloud Volumes Service for Google Cloud support SMB Direct?

No, SMB Direct is not currently supported.

What is the benefit of SMB Multichannel?

The SMB Multichannel feature enables an SMB3 client to establish a pool of connections over a single network interface card (NIC) or multiple NICs and to use them to send requests for a single SMB session. In contrast, by design, SMB1 and SMB2 require the client to establish one connection and send all the SMB traffic for a given session over that connection. This single connection limits the overall protocol performance from a single client.

Is there value in configuring multiple NICs on the SMB client?

Each Cloud Volumes Service volume is only attached to a single VPC network. Google Compute Engine VMs only support one NIC per VPC network. You can't configure multiple NICs to access a single Cloud Volumes Service volume.

Is NIC Teaming supported in Cloud Volumes Service for Google Cloud?

NIC Teaming is not supported in Cloud Volumes Service for Google Cloud. Although multiple network interfaces are supported on Google Cloud virtual machines, each interface is attached to a different VPC network. Also, the bandwidth available to a Google Cloud virtual machine is calculated for the machine itself and not any individual network interface.

What's the performance for SMB Multichannel?

SMB Multichannel only applies to volumes of the CVS-Performance service type.

The following tests and graphs demonstrate the power of SMB Multichannel on single-instance workloads.

Random I/O

With SMB Multichannel disabled on the client, 4-KiB read and write tests were performed using FIO and a 40-GiB working set. The SMB share was detached between each test, with increments of the SMB client connection count per RSS network interface settings of 1,4,8,6, set-SmbClientConfiguration-ConnectionCountPerRSSNetworkInterface count. The tests show that the default setting of 4 is sufficient for I/O intensive workloads; incrementing to 8 and 16 has no effect and as such has been left off of the following graph.

Bar chart showing difference in read and write IOPS with SMB Multichannel disabled and enabled.

During the test, the command netstat -na | findstr 445 shows that additional connections were established with increments from 1 to 4, to 8, and to 16. Four CPU cores were fully utilized for SMB during each test, as confirmed by the perfmon Per Processor Network Activity Cycles statistic (not included in this document.)

Sequential I/O

Tests similar to the random I/O tests were performed with 64-KiB sequential I/O. As with the random I/O tests, increasing the client connection count per RSS network interface beyond 4 had no noticeable effect on sequential I/O. The following graph compares the sequential throughput tests.

Bar chart showing difference in read and write throughput with SMB Multichannel disabled and enabled.

Therefore, it's best to follow the Microsoft best practice to use default RSS network tunables.

What test parameters were used to produce the performance graphs above?

The following configuration file was used with the Flexible IO (fio) load generator. Note that the iodepth parameter is marked as TBD. By increasing the iodepth value test by test, IO and throughput maximums were determined.

    directory=.\       #This is the directory where files are written
    direct=1           #Use directio
    numjobs=1          #To match how many users on the system
    nrfiles=4          #Num files per job
    runtime=300        #If time_based is set, run for this amount of time
    time_based         #This setting says run the jobs until run time elapses
    rw=rw||randrw      #choose rw if sequential io, choose randrw for random io
    rwmixread=100||0   #<-- Modify to get different i/o distributions
    iodepth=TBD        #<-- Modify this to get the i/o they want (latency * target op count)
    size=40G           #Aggregate file size per job (if nrfiles = 4, files=2.5GiB)
    ramp_time=20       #Warm up

What performance is expected with a single VM with a 1 TiB dataset?

SMB Multichannel only applies to volumes of the CVS-Performance service type.

To provide more detailed insight into workloads with read/write mixes, the following two charts show the performance of a single, Extreme service-level cloud volume of 50 TiB with a 1 TiB dataset and with an SMB multichannel of 4. An optimal IODepth of 16 was used, and Flexible IO (fio) parameters were used to ensure the full use of the network bandwidth (numjobs=16).

The following chart shows the results for 4k random I/O, with a single VM instance and a read/write mix at 10% intervals:

Random I/O

The following chart shows the results for sequential I/O:

Sequential I/O

What performance is expected when scaling out using 5 VMs with a 1 TiB dataset?

SMB Multichannel only applies to volumes of the CVS-Performance service type.

These tests with 5 VMs use the same testing environment as the single VM, with each process writing to its own file.

The following chart shows the results for random I/O:

Random I/O

The following chart shows the results for sequential I/O:

Sequential I/O

How do you monitor VirtIO ethernet adapters and ensure that you maximize network capacity?

One strategy used in testing with fio is to set numjobs=16. Doing so forks each job into 16 specific instances to maximize the Google VirtIO Ethernet Adapter.

You can check for activity on each of the adapters in Windows Performance Monitor by selecting Performance Monitor > Add Counters > Network Interface > Google VirtIO Ethernet Adapter.

Windows Performance Monitor

After you have data traffic running in your volumes, you can monitor your adapters in Windows Performance Monitor. If you do not use all of these 16 virtual adapters, you might not maximize your network bandwidth capacity.

Windows Performance Monitor

Are jumbo frames supported?

Jumbo frames are not supported with Compute Engine virtual machines.

What is SMB Signing, and is it supported by Cloud Volumes Service for Google Cloud?

The SMB protocol provides the basis for file and print sharing and other networking operations such as remote Windows administration. To prevent man-in-the-middle attacks that modify SMB packets in transit, the SMB protocol supports the digital signing of SMB packets.

SMB Signing is supported for all SMB protocol versions that are supported by Cloud Volumes Service for Google Cloud.

What is the performance impact of SMB Signing?

SMB Signing has a detrimental effect upon SMB performance. Among other potential causes of the performance degradation, the digital signing of each packet consumes additional client-side CPU. In this case, Core 0 appears responsible for SMB, including SMB Signing. A comparison using the CVS-Performance service type with the non-multichannel sequential read throughput numbers from the sequential I/O section shows that SMB Signing reduces overall throughput from 875 MiB/s to approximately 250 MiB/s.

Capacity management FAQs

This section provides answers to FAQs about the capacity-management elements of the Cloud Volumes Service for Google Cloud.

How do I determine if a directory is approaching the limit size?

You can use the stat command from a Cloud Volumes Service client to see whether a directory is approaching the maximum size limit (320 MB).

For a 320 MB directory, the number of 512-byte blocks is 655360 (320x1024x1024/512).


[makam@cycrh6rtp07 ~]$ stat bin
File: 'bin'
Size: 4096            Blocks: 8          IO Block: 65536  directory

[makam@cycrh6rtp07 ~]$ stat tmp
File: 'tmp'
Size: 12288           Blocks: 24         IO Block: 65536  directory

[makam@cycrh6rtp07 ~]$ stat tmp1
File: 'tmp1'
Size: 4096            Blocks: 8          IO Block: 65536  directory

Billing FAQs

This section provides answers to billing-related FAQs about the Cloud Volumes Service for Google Cloud.

Will I be billed for accessing my cloud volume from a Compute Engine instance located in a different region or zone?

Yes, standard Google Cloud inter-region data movement is charged according to the transfer rates.

  • CVS service-type volumes: If your Compute Engine instance is located within the same zone as the cloud volume, you are not charged for any traffic movement. If your Compute Engine instance is located in a different zone than the cloud volume, you are charged for traffic movement between zones.

  • CVS-Performance service-type volumes: If your Compute Engine instance is located within the same region as the cloud volume, you are not charged for any traffic movement, even if that movement occurs within different zones in a region.