Linux Logical Volume Manager (LVM) is a common general-purpose storage manager in all popular Linux distributions. When working with the LVM and ME5 storage systems, LVM mirroring is not necessary because storage protection is already provided by the different RAID levels within the storage system. An LVM volume group is a collection of one or more LUNs created on the ME5 volumes. Logical volumes are created that span across the LUNs within the volume group.
LVM guidelines
Dell Technologies recommends the following LVM guidelines:
- Use whole LUNs for logical volume groups.
- Create separate volume groups for different applications data. For example, if there are two databases, separate the databases into logical volume groups. This simplifies management and allows greater flexibility on array-based snapshots on individual applications.
- It is common to use two or more LUNs in a volume group to increase capacity and improve performance. All LUNs in a volume group should be of the same size. To realize the full performance benefit, evenly distribute the LUNs in different ME5 storage pools, disk groups, and across the two controllers.
- When using ME5 volume snapshots to protect the data in a logical volume group, the snapshots must be taken on all LUNs in the same volume group simultaneously to guarantee the consistency of the data. It is a best practice to pause/stop the applications that are accessing the LUNs before taking any snapshots.
- Snapshot schedules can be created on individual volumes in PowerVault Manager. It is not possible to create a schedule against a group of volumes. Therefore, it becomes a challenge to coordinate taking consistent snapshots for multiple volumes. One option is to write a script that incorporates the necessary steps to take a consistent snapshot. ME5 storage system provides a full-feature command-line interface (CLI) that allows administrators to remotely manage and automate storage tasks.
Create LVM volume group and set physical volume data alignment
It might be necessary to specify data alignment on LVM physical volumes (PV) to avoid data misalignment. Because the ME5 storage system uses an internal chunk size ranging from 64k to 512k, it is recommended to initialize LVM PV with a 1 MB alignment. Use pvcreate --dataalignment 1m to indicate that the alignment starts at 1 MB.
# pvcreate –-dataalignment 1m /dev/mapper/mpathb
# vgcreate /dev/vgapp /dev/mapper/mpathb
# lvcreate -l 83444 -n lvapp vgapp
Expand storage for LVM
Adding capacity to an existing LVM volume group can be performed in one of two ways:
- Create ME5 volumes and initialize them into the LVM volume group. It is recommended that the new volumes be of equal capacity and have the same back-end storage type as the existing volumes in the volume group. When the volume group is expanded, the logical volume can be resized to take up the new capacity. The advantage of this method is that existing volumes are not changed. Only new volumes are introduced in the environment and can be backed out easily.
- Dynamically increase the size of existing ME5 volumes in PowerVault Manager. The ME5 storage system can resize the virtual volumes without causing any application interruptions. On the Linux host, resize the physical and multipath devices on the operating system, and then resize the logical volume and file system. Depending on the file system type, the resize tasks can be done online without disrupting the applications. The section Expand storage for the file system provides an example of this procedure. This method involves fewer administrative tasks because there are no new volumes, new mappings, new snapshot schedules, or new LVM physical devices to manage and set up.