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Chapter 1. Available storage options overview

There are several local, remote, and cluster-based storage options available on Red Hat Enterprise Linux 8.

Local storage implies that the storage devices are either installed on the system or directly attached to the system.

With remote storage, devices are accessed over LAN, the internet, or using a Fibre channel network. High Level Red Hat Enterprise Linux Storage Diagram describes the different storage options.

Figure 1.1. High Level Red Hat Enterprise Linux Storage Diagram

High Level RHEL Storage Diagram

1.1. Local storage overview

Red Hat Enterprise Linux 8 offers several local storage options.

Basic disk administration

Using parted and fdisk, you can create, modify, delete, and view disk partitions. The following are the partitioning layout standards:

Master Boot Record (MBR)
It is used with BIOS-based computers. You can create primary, extended, and logical partitions.
GUID Partition Table (GPT)
It uses Globally Unique identifier (GUID) and provides unique disk and partition GUID.

To encrypt the partition, you can use Linux Unified Key Setup-on-disk-format (LUKS). To encrypt the partition, select the option during the installation and the prompt displays to enter the passphrase. This passphrase unlocks the encryption key.

Storage consumption options
Non-Volatile Dual In-line Memory Modules (NVDIMM) Management
It is a combination of memory and storage. You can enable and manage various types of storage on NVDIMM devices connected to your system.
Block Storage Management
Data is stored in the form of blocks where each block has a unique identifier.
File Storage
Data is stored at file level on the local system. These data can be accessed locally using XFS (default) or ext4, and over a network by using NFS and SMB.
Logical volumes
Logical Volume Manager (LVM)

It creates logical devices from physical devices. Logical volume (LV) is a combination of the physical volumes (PV) and volume groups (VG). Configuring LVM include:

  • Creating PV from the hard drives.
  • Creating VG from the PV.
  • Creating LV from the VG assigning mount points to the LV.
Virtual Data Optimizer (VDO)

It is used for data reduction by using deduplication, compression, and thin provisioning. Using LV below VDO helps in:

  • Extending of VDO volume
  • Spanning VDO volume over multiple devices
Local file systems
XFS
The default RHEL file system.
Ext4
A legacy file system.
Stratis
It is available as a Technology Preview. Stratis is a hybrid user-and-kernel local storage management system that supports advanced storage features.

1.2. Remote storage overview

Following are the remote storage options available in Red Hat Enterprise Linux 8:

Storage connectivity options
iSCSI
RHEL 8 uses the targetcli tool to add, remove, view, and monitor iSCSI storage interconnects.
Fibre Channel (FC)

Red Hat Enterprise Linux 8 provides the following native Fibre Channel drivers:

  • lpfc
  • qla2xxx
  • Zfcp
Non-volatile Memory Express (NVMe)

An interface which allows host software utility to communicate with solid state drives. Use the following types of fabric transport to configure NVMe over fabrics:

  • NVMe over fabrics using Remote Direct Memory Access (RDMA).
  • NVMe over fabrics using Fibre Channel (FC)
Device Mapper multipathing (DM Multipath)
Allows you to configure multiple I/O paths between server nodes and storage arrays into a single device. These I/O paths are physical SAN connections that can include separate cables, switches, and controllers.
Network file system
  • NFS
  • SMB

1.3. GFS2 file system overview

The Red Hat Global File System 2 (GFS2) file system is a 64-bit symmetric cluster file system which provides a shared name space and manages coherency between multiple nodes sharing a common block device. A GFS2 file system is intended to provide a feature set which is as close as possible to a local file system, while at the same time enforcing full cluster coherency between nodes. To achieve this, the nodes employ a cluster-wide locking scheme for file system resources. This locking scheme uses communication protocols such as TCP/IP to exchange locking information.

In a few cases, the Linux file system API does not allow the clustered nature of GFS2 to be totally transparent; for example, programs using POSIX locks in GFS2 should avoid using the GETLK function since, in a clustered environment, the process ID may be for a different node in the cluster. In most cases however, the functionality of a GFS2 file system is identical to that of a local file system.

The Red Hat Enterprise Linux (RHEL) Resilient Storage Add-On provides GFS2, and it depends on the RHEL High Availability Add-On to provide the cluster management required by GFS2.

The gfs2.ko kernel module implements the GFS2 file system and is loaded on GFS2 cluster nodes.

To get the best performance from GFS2, it is important to take into account the performance considerations which stem from the underlying design. Just like a local file system, GFS2 relies on the page cache in order to improve performance by local caching of frequently used data. In order to maintain coherency across the nodes in the cluster, cache control is provided by the glock state machine.

Additional resources

1.4. Gluster Storage overview

The Red Hat Gluster Storage (RHGS) is a software-defined storage platform that can be deployed in clusters. It aggregates disk storage resources from multiple servers into a single global namespace. GlusterFS is an open source distributed file system that is suitable for cloud and hybrid solutions.

Volumes form the base for GlusterFS and provide different requirements. Each volume is a collection of bricks, which are basic units of storage that are represented by an export directory on a server in the trusted storage pool.

The following types of GlusterFS volumes are available:

  • Distributed GlusterFS volume is the default volume where each file is stored in one brick and the file cannot be shared between different bricks.
  • Replicated GlusterFS volume type replicates user data, so that if one brick fails, the data is still accessible.
  • Distributed replicated GlusterFS volume is a hybrid volume that distributes replicas over a large number of systems. It is suitable for environments where storage scalability and high-reliability are critical.

1.5. Ceph Storage overview

Red Hat Ceph Storage (RHCS) is a scalable, open, software-defined storage platform that combines the most stable version of the Ceph storage system with a Ceph management platform, deployment utilities, and support services.

Red Hat Ceph Storage is designed for cloud infrastructure and web-scale object storage. Red Hat Ceph Storage clusters consist of the following types of nodes:

Red Hat Ceph Storage Ansible administration node

This type of node acts as the traditional Ceph Administration node did for previous versions of Red Hat Ceph Storage. This type of node provides the following functions:

  • Centralized storage cluster management
  • The Ceph configuration files and keys
  • Optionally, local repositories for installing Ceph on nodes that cannot access the Internet for security reasons
Monitor nodes

Each monitor node runs the monitor daemon (ceph-mon), which maintains a copy of the cluster map. The cluster map includes the cluster topology. A client connecting to the Ceph cluster retrieves the current copy of the cluster map from the monitor which enables the client to read from and write data to the cluster.

Important

Ceph can run with one monitor; however, to ensure high availability in a production cluster, Red Hat will only support deployments with at least three monitor nodes. Red Hat recommends deploying a total of 5 Ceph Monitors for storage clusters exceeding 750 OSDs.

OSD nodes

Each Object Storage Device (OSD) node runs the Ceph OSD daemon (ceph-osd), which interacts with logical disks attached to the node. Ceph stores data on these OSD nodes.

Ceph can run with very few OSD nodes, which the default is three, but production clusters realize better performance beginning at modest scales, for example 50 OSDs in a storage cluster. Ideally, a Ceph cluster has multiple OSD nodes, allowing isolated failure domains by creating the CRUSH map.

MDS nodes
Each Metadata Server (MDS) node runs the MDS daemon (ceph-mds), which manages metadata related to files stored on the Ceph File System (CephFS). The MDS daemon also coordinates access to the shared cluster.
Object Gateway node
Ceph Object Gateway node runs the Ceph RADOS Gateway daemon (ceph-radosgw), and is an object storage interface built on top of librados to provide applications with a RESTful gateway to Ceph Storage Clusters. The Ceph Object Gateway supports two interfaces:
S3
Provides object storage functionality with an interface that is compatible with a large subset of the Amazon S3 RESTful API.
Swift
Provides object storage functionality with an interface that is compatible with a large subset of the OpenStack Swift API.

Additional resources