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Volume management
28 Dell EMC SC Series: Red Hat Enterprise Linux Best Practices | CML1031
Create and label a filesystem:
# mkfs.ext4 –L testfs /dev/mapper/testvol1
3.8 Linux LVM
Linux Logical Volume Manager (LVM) is a common general-purpose storage manager included in all popular
Linux distributions. It provides application-level mirroring and RAID striping, but they are not necessary when
the SC Series volumes are used because storage protection is already provided by the SC Series array. Data
is periodically rebalanced on the SC Series array automatically to optimize performance and availability. LVM-
level mirroring and RAID striping can be done manually upon creation. However, data is not rebalanced when
the volume groups and logical volumes are expanded. Administrators must manually perform the rebalance
on LVM.
Multiple LUNs can be grouped into a single LVM volume group. Then, logical volumes must be created that
span across these LUNs. When taking SC Series snapshots on a multi-LUN volume group, ensure the LUNs
are configured in a consistency group.
A filesystem is typically created on a logical volume where the application is then installed in the filesystem.
Additional space can be added to the volume groups, logical volumes, and filesystems either by adding new
LUNs or by expanding existing LUNS in the volume groups. Once volume groups and logical volumes are
expanded, the file systems can be resized to the newly added space. LVM and many popular file systems
such as ext4 and xfs allow on-demand expansion without taking down the applications.
The following LVM guidelines are recommended:
• Use whole LUNs for volume groups.
• Create a dedicated volume group for storing each copy or version of application. This simplifies
management and allows greater flexibility on array-based snapshots.
• Use two or more LUNs in a volume group when performance is of concern. This allows more I/O
streams and the use of both SC Series controllers.
• Configure all LUNs with the same size in the same volume group and group them in the same
consistency group.
3.8.1 Physical volume data alignment
The data alignment detection is enabled by default in the /etc/lvm/lvm.conf file. If the Linux operating system
has trouble determining the data alignment, use the --dataalignment argument to indicate the alignment
starts at 1M when initializing LUNs in LVM.
The following example shows the tasks to create a file system on LVM:
# pvcreate --dataalignment 1m /dev/mapper/testvol
# vgcreate vgapp /dev/mapper/testvol
# lvcreate –L 5g –n lvapp vgapp
# mkfs.xfs –L appfs /dev/vgapp/lvapp (for xfs)
# mkfs.ext4 –L appfs /dev/vgapp/lvapp (for ext4)