Now, let’s talk about the storage domains. In Oracle Linux Virtualization Manager, a storage domain is a fundamental concept that represents a logical storage container where various virtualization related data is stored. Let’s try to understand how it is done. Have a common storage interface.
So a storage domain provides a standardized interface through which virtualization components interact with storage resources. This interface abstracts the underlying storage technologies like NFS, GlusterFS, iSCSI, FCP and allows the OLVM to manage and utilize storage resources uniformly.
Contain complete images of templates, VM, snapshots, and ISO files. So basically, storage domain in OLVM will contain the images of various components, like it can be a part containing templates, pre-configured VM templates, which can be used for rapid deployment of your virtual machines or VMs, which are like virtual machine disk images that store operating system, application, and data.
It also stores snapshots, which is point in time copies of your VM disks, ISO files that can be disk images used for installing operating systems or applications on virtual machines.
OLVM support storage domains that are block device storage domains and file system storage domains. Like in block devices, it supports SAN, which is iSCSI or FCP. And in File systems, it supports NAS which is NFS or Gluster file system.
So if I go with the block devices, which is a SAN storage style, iSCSI uses the internet small computer system interface protocol to provide block level access to storage volumes, and that is provided over your IP networks. The Fiber Channel protocol provides block level access to storage volumes over fiber channel networks, offering high speed, low latency storage access.
With file system NAS type network access to storage, which is consisting of NFS, which is the storage is over a network sharing files and directories as if they are mounted locally. And GlusterFS is a distributed file system that allows OLVM hosts to access storage distributed across multiple servers.
Virtual machines should share the same storage domain to be migrated. Again, storage domains helps in migration and sharing. So virtual machines using OLVM can be migrated between hosts within the same data center. For successful migration, the source and destination host must have access to the same storage domain where the VM disk image is residing.
It also supports– the data center can have at least one data domain. The data center requirements are basically categorized as non shared between data centers data domain. So a data domain is actually a domain that is created for each data center. It cannot be shared between data centers.
So every data center must have at least one storage domain attached to it. And this ensures that there is a dedicated storage location for storing your VM data, and it cannot be shared between your data centers. So it’s non shared between data centers. So storage domains cannot be shared between different OLVM data centers and each data center manages its own set of storage domains to maintain isolation and control over storage resources.
Now, let’s talk about something called as storage pool manager, which is also termed as the SPM. The storage pool manager plays a crucial role in managing storage domains within a data center. So let’s try to see how does the storage pool manager help managing your storage domains.
SPM is a management role assigned to one of the host in the data center. So the role is assigned to one of the host within a data center by the OLVM engine. The host acts as a designated SPM for that particular data center.
It manages the storage domains of the data center. The SPM is responsible for managing the storage domains within the data center. This includes coordinating access to storage resources and ensuring the integrity of storage metadata across all storage domains.
And it also works with controlling access to storage by coordinating the metadata between the storage domains. SPM controls access to these storages by controlling and coordinating the metadata between storage domains or metadata includes information about virtual machines, disk images, templates, snapshots, and other virtualization related data which is stored inside your storage domain.
The host running as SPM can still host virtual resources, so it’s not like the host, which is acting like SPM is only managing storage domain, but it can also host its own virtual resources. The SPM role is a primary role involving managing storage.
The host running the SPM can still host virtual resources such as virtual machines and their applications. This ensures that the host contributes to both storage management and a compute resource within the data center.
Now, what happens if the host is affected? So the engine assigns the role to another host, if the SPM host becomes unavailable. So there is a failover mechanism that is done internally. If the host currently serving as the SPM becomes unavailable due to hardware failure, network issues or other reasons, the OLVM engine automatically assigns the SPM role to another host within that particular data center.
And the failover mechanism ensures continuity in storage management operations with minimizing disruptions in virtualized environments. So basically, internal failure mechanism is handled when the engine or the host becomes unavailable.
Now, there’s something which is called as storage lease. So basically, a storage lease is a mechanism that enables virtual machines to maintain consistent access to storage across different host within a data center. Let’s try to see how does it work.
When you add a storage domain, a special volume is created called as the xlease volume. And virtual machines are able to acquire a lease on this special volume. So special volume is created when you define this particular storage lease.
When you add a storage domain to an OLVM, a volume called xlease is automatically created within the storage domain. And this volume is designated for managing storage leases for VMs, and the virtual machines are able to acquire a lease on this particular special volume.
So virtual machines have the capability to acquire a lease on the xlease volume within their associated storage domain. This lease mechanism ensures that VM can maintain exclusive access to their required storage resources.
A storage lease is configured automatically for the virtual machines on selecting storage domains to hold the VM lease. So when configuring a virtual machine and selecting a storage domain to hold its disk, images, and related resources, OLVM will automatically configure a storage lease for that VM.
This lease allows the VM to start and operate on any host within that data center that has access to the storage domain holding that lease. It also gives you the options to enabling mobility, so it enables virtual machines to start on another host. So storage leads is supporting the virtual machines to get migrated and started on the other host doors.
The lease ID and other information are sent from the SPM to the engine. So the transmission of lease information for those virtual machines is handled by your SPM. All plays a key role in managing storage leases with storage pool manager.
It communicates lease IDs and related information to the OLVM engine, which maintains a record of each VM device, list along with the information about the VM machine, the disk image that is used, and the lease that is allocated to that particular virtual machine. This is actually used and supporting the migration of virtual machines from one host to the other host.
Now, when you learn about storage SPM lease, let’s also talk a little bit about the virtual machine storage. The virtual machine storage you’ll get more detail about it in the module where we’ll talking about the managing virtual machines. But here we are just going to get into a very basic understanding of virtual machine storage.
So the virtual machine storage is basically a way of assigning or managing disk resources efficiently that are allocated to your virtual machines. So they are some important points to remember here. It is a thin provisioned virtual disk by default. So default provisioning is basically a thin provisioned disk. This means that the virtual disk starts small and grow dynamically as the data is written to it.
If you are using iSCSI storage or other block based devices, logical unit numbers are provided to the SPM to handle it. So the SPM will take the LUNs, which represent the block level storage volumes that OLVM host access over the network.
The virtual disk is pre-allocated by default. So basically, a pre-allocated in provisioned disk which allows the administrator to choose a pre-allocated virtual disk for VM. So pre-allocated disk reserves the entire disk space upfront.
So you can also go with configuring a pre-allocated virtual disk if I want to go with the options of enabling the disk option. So if I’m using the type of raw disk or go to version disk, then I can decide on specifying a virtual disk that is a pre-allocated virtual disk that can be used as a storage disk for your virtual machines.
Use pre-allocated disks within high levels of I/O. If you are having a high level of input/outputs we would suggest to use your pre-allocated disk which will allocate the complete disk to your virtual machine. The VM host continuously monitors the logical volume usage, so VM host is continuously monitoring the usage of the logical volume associated with their virtual disk. And this monitoring ensures that the administrators can track storage usage trends, identify potential capacity issues, and manage storage resources effectively.
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