Building Resilient and Flexible Storage: Combining LVM with Multipath on RHEL
In the world of enterprise IT, reliable and flexible storage is paramount. System administrators constantly seek ways to ensure data availability, improve performance, and simplify storage management. Two powerful technologies on Red Hat Enterprise Linux (RHEL) that address these needs are Logical Volume Management (LVM) and Multipath I/O. When used together, they create a robust storage foundation that is both highly available and remarkably flexible.
Let’s break down why this combination is so effective and how it works.
Understanding the Building Blocks
First, a quick look at the individual components:
Logical Volume Management (LVM): LVM provides an abstraction layer over physical storage devices (like hard drives or SAN LUNs). Instead of working directly with raw disks, you create Physical Volumes (PVs) from them, group these PVs into Volume Groups (VGs), and then carve out Logical Volumes (LVs) from the VGs. This offers immense flexibility:
- Easy Resizing: Logical volumes can be grown or shrunk with relative ease.
- Snapshots: LVM supports creating snapshots of logical volumes for backups or testing.
- Striping and Mirroring: LVM allows for data striping across multiple physical devices for performance or mirroring for redundancy.
- Simplified Management: Administrating storage becomes much simpler, even as physical hardware changes.
Multipath I/O: In modern data centers, servers often connect to storage arrays via multiple physical paths (e.g., multiple Fibre Channel or iSCSI cables, redundant network switches, multiple HBA cards). Without multipath, the operating system might see the same physical disk presented as multiple separate devices (like
/dev/sda,/dev/sdb,/dev/sdc), potentially leading to data corruption or making it difficult to use the storage reliably. Multipath solves this by:- Consolidating Paths: It aggregates these multiple paths into a single logical device name (typically found under
/dev/mapper/). - **Providing **Fault Tolerance: If one path fails (e.g., a cable is unplugged or a switch fails), I/O can automatically reroute over the remaining paths, ensuring continuous access to storage.
- Improving Performance: I/O operations can be load-balanced across the available paths, increasing throughput.
- Consolidating Paths: It aggregates these multiple paths into a single logical device name (typically found under
The Power of Combination
Combining LVM and Multipath is a best practice for critical storage on RHEL, especially when connected to SAN or network storage.
The magic happens when you use the multipath device names (from /dev/mapper/) as the underlying physical devices (PVs) for your LVM setup. Instead of creating an LVM physical volume on a single path like /dev/sda, you create it on the stable, fault-tolerant multipath device, like /dev/mapper/your-san-lun-id.
This synergy means:
- Storage Resilience: Your LVM volumes are built on a foundation that is resilient to individual path failures. If an HBA goes bad or a cable is cut, the LVM volumes built on that multipathed device remain accessible via the other paths.
- Flexible High-Availability: You get all the benefits of LVM’s flexibility (easy resizing, snapshots) combined with the underlying high availability provided by multipath.
- Consistent Device Naming: The
/dev/mapper/names provided by multipath are persistent across reboots and path changes, making LVM configuration stable and predictable.
Key Steps in Configuration (Actionable Advice)
While the detailed steps can vary based on your storage hardware and RHEL version, the general process involves:
- Install and Configure Multipath: Ensure the
device-mapper-multipathpackage is installed. Configure/etc/multipath.confto recognize your storage devices and set up appropriate path selectors and failover policies. This is a critical first step. - Scan for Devices: Use commands like
multipath -v2ormultipath -llto scan for and verify that your storage devices are being correctly recognized and aggregated under/dev/mapper/. Ensure the status is active. - Use Multipath Devices for LVM: Now, and only now, use the
/dev/mapper/names as the physical devices when creating LVM physical volumes:pvcreate /dev/mapper/your-san-lun-id. - Create Volume Groups and Logical Volumes: Proceed with standard LVM configuration, creating volume groups from your multipathed physical volumes and then creating logical volumes from those volume groups.
- Create Filesystems and Mount: Format your logical volumes and mount them as needed.
Important Tip: Always refer to the multipath device names (/dev/mapper/...) when performing LVM operations on storage configured with multipath. Never use the underlying /dev/sdX names directly for LVM on such devices.
Conclusion
Configuring LVM with Multipath on RHEL is a fundamental strategy for building reliable, flexible, and high-performance storage solutions. It ensures that your data volumes can withstand path failures while providing the easy management and dynamic resizing capabilities that LVM is known for. By leveraging these technologies together, you create a robust storage infrastructure that is well-suited for demanding enterprise workloads.
Source: https://infotechys.com/configure-lvm-on-multipath-devices-in-rhel/
