Attaching a Volume to Multiple Instances

The Oracle Cloud Infrastructure Block Volume service provides the capability to attach a block volume to multiple Compute instances. With this feature, you can share block volumes across instances in read/write or read-only mode. Attaching block volumes as read/write and shareable enables you to deploy and manage your cluster-aware solutions.

This topic describes how to attach block volumes as shareable, along with the limits and considerations for this feature.

See Volume Access Types for more information about the available access type options. For attaching volumes to single instances, see Attaching a Volume.

Limits and Considerations

  • The Block Volume service does not provide coordination for concurrent write operations to block volumes attached to multiple instances, so if you configure the block volume as read/write and shareable you must deploy a cluster aware system or solution on top of the shared storage, see Configuring Multiple Instance Volume Attachments with Read/Write Access.

  • Once you attach a block volume to an instance as read-only, it can only be attached to other instances as read-only. If you want to attach the block volume to an instance as read/write, you need to detach the block volume from all instances and then you can reattach the block volume to instances as read/write.

  • If the block volume is already attached to an instance as read/write non-shareable you can't attach it to another instance until you detach it from the first instance. You can then reattach it to both the first and second instances as read/write shareable.

  • You can't delete a block volume until it has been detached from all instances it was attached to. When viewing the instances attached to the block volume from the Resources section of the Volume Details page, you should note that only instances in the selected compartment will be displayed. You may need to change the compartment to list additional instances that are attached to the volume.

  • You can attach a block volume as read/write shareable or read-only shareable up to a maximum of eight instances.

  • Block volumes attached as read-only are configured as shareable by default.

  • Performance characteristics described in Block Volume Performance are per volume, so when a block volume is attached to multiple instances the performance is shared across all the attached instances.

Configuring Multiple Instance Volume Attachments with Read/Write Access

The Block Volume service does not provide coordination for concurrent write operations to volumes attached to multiple instances. To prevent data corruption from uncontrolled read/write operations you must install and configure a cluster aware system or solution such as Oracle Cluster File System version 2 (OCFS2) on top of the shared storage before you can use the volume.

You can see an sample walkthrough of scenario using OCFS2 described in Using the Multiple-Instance Attach Block Volume Feature to Create a Shared File System on Oracle Cloud Infrastructure. The summary of the required steps for this scenario are:

  1. Attach the block volume to an instance as Read/Write-Shareable using the Console, CLI, or API.

  2. Set up your OCFS2/O2CB cluster nodes.

  3. Create your OCFS2 file system and mount point.

Required IAM Policy

To use Oracle Cloud Infrastructure, you must be granted security access in a policy  by an administrator. This access is required whether you're using the Console or the REST API with an SDK, CLI, or other tool. If you get a message that you don’t have permission or are unauthorized, verify with your administrator what type of access you have and which compartment  you should work in.

For administrators: The policy in Let users launch Compute instances includes the ability to attach/detach existing block volumes. The policy in Let volume admins manage block volumes, backups, and volume groups lets the specified group do everything with block volumes and backups, but not launch instances.

If you're new to policies, see Getting Started with Policies and Common Policies. For reference material about writing policies for instances, cloud networks, or other Core Services API resources, see Details for the Core Services.

Using the Console

To attach a volume to multiple instances from the Instance details page
  1. Open the navigation menu. Under Core Infrastructure, go to Compute and click Instances.
  2. In the Instances list, click the instance that you want to attach a volume to.

  3. In the Resources section, click Attached Block Volumes.

  4. Click Attach Block Volume.

  5. Select the volume attachment type, iSCSI or Paravirtualized.

    For more information, see Volume Attachment Types.

  6. Select the volume access type. Select Read/Write-Shareable if you want to enable read/write attachments to multiple instances or Read-only-Shareable for read-only attachments to multiple instances.

    For more information, see Volume Access Types.

  7. In the Block Volume Compartment drop-down list, select the compartment.

  8. Specify the volume you want to attach to. To use the volume name, choose SELECT VOLUME and then select the volume from the Block Volume drop-down list. To specify the volume OCID, choose ENTER VOLUME OCID and then enter the OCID into the Block Volume OCID field.

  9. If the instance supports consistent device paths select a path from the Device Path drop-down list when attaching. This is required and enables you to specify a device path for the volume attachment that remains consistent between instance reboots.

    For more information about this feature and the instances that support it, see Connecting to Volumes With Consistent Device Paths

    Tip

    You must select a device path when you attach a volume from the Console, it is not optional. Specifying a device path is optional when you attach a volume using the CLI, REST APIs, or SDK.
  10. For paravirtualized volume attachments on virtual machine (VM) instances, you can optionally encrypt data that is transferred between the instance and the Block Volume service storage servers. To do this, select the Use in-transit encryption check box. If you configured the volume to use an encryption key that you manage using the Vault service, this key is used for in-transit encryption. Otherwise, the Oracle-provided encryption key is used. See Block Volume Encryption for more information.

  11. Click Attach.

    When the volume's icon no longer lists it as Attaching, if the attachment type is Paravirtualized, you can use the volume. If the attachment type is iSCSI, you need to connect to the volume first. For more information, see Connecting to a Volume.

    On Linux-based instances, if you want to automatically mount volumes on instance boot, you need to set some specific options in the /etc/fstab file, or the instance may fail to launch. This applies to both iSCSI and paravirtualized attachment types. For volumes using consistent device paths, see fstab Options for Block Volumes Using Consistent Device Paths. For all other volumes, see Traditional fstab Options.

To attach a volume to multiple instances from the Block Volume details page
  1. Open the navigation menu. Under Core Infrastructure, go to Block Storage and click Block Volumes.
  2. In the Block Volumes list, click the block volume that you want to attach to an instance.

  3. In the Resources section, click Attached Instances.

  4. Click Attach to Instance.

  5. Select the volume attachment type, iSCSI or Paravirtualized.

    For more information, see Volume Attachment Types.

  6. Select the volume access type. Select Read/Write-Shareable if you want to enable read/write attachments to multiple instances or Read-only-Shareable for read-only attachments to multiple instances.

    For more information, see Volume Access Types.

  7. In the Choose Instance drop-down list, select the instance. Click Change Compartment if the instance is in a different compartment than the default one listed. If you want to specify the instance using the OCID, select the ENTER INSTANCE OCID option and then copy the OCID in the textbox.

  8. If the instance supports consistent device paths select a path from the Device Path drop-down list when attaching. This is required and enables you to specify a device path for the volume attachment that remains consistent between instance reboots.

    For more information about this feature and the instances that support it, see Connecting to Volumes With Consistent Device Paths

    Tip

    You must select a device path when you attach a volume from the Console, it is not optional. Specifying a device path is optional when you attach a volume using the CLI, REST APIs, or SDK.
  9. For paravirtualized volume attachments on virtual machine (VM) instances, you can optionally encrypt data that is transferred between the instance and the Block Volume service storage servers. To do this, select the Use in-transit encryption check box. If you configured the volume to use an encryption key that you manage using the Vault service, this key is used for in-transit encryption. Otherwise, the Oracle-provided encryption key is used. See Block Volume Encryption for more information.

  10. Click Attach.

    When the volume's icon no longer lists it as Attaching, if the attachment type is Paravirtualized, you can use the volume. If the attachment type is iSCSI, you need to connect to the volume first. For more information, see Connecting to a Volume.

    On Linux-based instances, if you want to automatically mount volumes on instance boot, you need to set some specific options in the /etc/fstab file, or the instance may fail to launch. This applies to both iSCSI and paravirtualized attachment types. For volumes using consistent device paths, see fstab Options for Block Volumes Using Consistent Device Paths. For all other volumes, see Traditional fstab Options.

To view the instances attached to a volume from the Volume details page
  1. Open the navigation menu. Under Core Infrastructure, go to Block Storage and click Block Volumes.
  2. In the Block Volumes list, click the block volume that you want to view the attached instances for.

  3. In the Resources section, click Attached Instances.

All the attached instances in the selected compartment will be displayed in the list. To view attached instances in other compartments, change the compartment in the COMPARTMENT drop down list.

To view the volumes attached to an instance from the Instance details page
  1. Open the navigation menu. Under Core Infrastructure, go to Compute and click Instances.
  2. In the Instances list, click the instance that you want to view the attached volumes for.

  3. In the Resources section, click Attached Block Volumes.

All the block volumes attached to the instance will be displayed in the list, regardless of the compartment the block volumes are in.

Using the CLI

For information about using the CLI, see Command Line Interface (CLI).

To attach a volume to an instance as shareable, read/write

Open a command prompt and run:

oci compute volume-attachment attach --instance-id <instance_ID> --type <attachment_type> --volume-id <volume_ID>  --read-only true/false  --is-shareable true

For example:

oci compute volume-attachment attach --instance-id ocid1.instance.oc1..<unique_ID> --type iscsi --volume-id ocid1.volume.oc1..<unique_ID> --read-only false --is-shareable true
To list all the instances attached to a volume

Open a command prompt and run:

oci compute volume-attachment list --compartment-id <compartment_ID> --volume-id <volume_ID>

For example:

oci compute volume-attachment attach --compartment-id ocid1.compartment.oc1..<unique_ID> --volume-id ocid1.volume.oc1..<unique_ID>
Note

This operation will only return the attached instances that are in the specified compartment. You need to run this operation for every compartment that may contain instances that are attached to the specified volume.

Using the API

Use the following APIs to attach volumes and work with volume attachments to instances:

For information about using the API and signing requests, see REST APIs and Security Credentials. For information about SDKs, see Software Development Kits and Command Line Interface.

Additional Resources

See the following links for example deployments of shared file systems on Oracle Cloud Infrastructure.