This chapter describes the following major topics:

[ {.c37}]{.c36}Describe Logical Volume Manager and its components

[ {.c37}]{.c36}Understand various Logical Volume Manager management operations

[ {.c37}]{.c36}Know Logical Volume Manager administration commands

[ {.c37}]{.c36}Create and confirm physical volumes, volume groups, and logical volumes

[ {.c37}]{.c36}Rename, reduce, extend, and remove logical volumes

[ {.c37}]{.c36}Extend, reduce, and remove volume groups

[ {.c37}]{.c36}Remove physical volumes

[ {.c37}]{.c36}Overview of Stratis (a volume-managing file system solution in RHEL) service and how it works

[ {.c37}]{.c36}Understand various Stratis management operations and the command

[ {.c37}]{.c36}Create, confirm, expand, rename, and destroy pools and file systems

[RHCSA Objectives:]{.c39}

[28]{#part0026_split_000.html#id_794 .calibre10}[.]{.c29}Create and remove physical volumes

[29]{#part0026_split_000.html#id_795 .calibre10}[.]{.c29}Assign physical volumes to volume groups

[30]{#part0026_split_000.html#id_796 .calibre10}[.]{.c29}Create and delete logical volumes

32[.]{.c29}Add new partitions and logical volumes, and swap to a system non-destructively (the swap portion of this objective is covered in Chapter 15)

[35]{#part0026_split_000.html#id_801 .calibre10}[.]{.c29}Extend existing logical volumes (additional coverage on this objective is available in Chapter 15)

[38]{#part0026_split_000.html#id_804 .calibre10}[.]{.c29}Manage layered volumes

::: {#part0026_split_000.html#calibre_pb_1 .calibre12} :::

[]{#part0026_split_001.html}

[ T]{.c42}[his]{.c43} chapter is the second of the three chapters (the other two being Chapter 13{.calibre5} (previous) and Chapter 15{.calibre5} (next)) that expounds upon storage management concepts and solutions available in RHEL. We discussed partitioning and thinly provisioned volumes in the previous chapter. This chapter presents a detailed coverage on Logical Volume Manager solution. LVM sets up an abstraction layer between the operating system and the storage hardware. It utilizes virtual objects for storage pooling and allocation, and offers a whole slew of management commands, each of which carries out a particular operation.

The other advanced storage management solution discussed in this chapter is a volume-managing file system that capitalizes on the proven features of LVM and the kernel device driver software. This solution dynamically adjusts the size of the underlying volume, eliminating the need for manual expansion.

[Logical]{#part0026_split_001.html#id_379 .calibre10} Volume Manager (LVM)

The Logical Volume Manager (LVM) solution is widely used for managing block storage in Linux. LVM provides an abstraction layer between the physical storage and the file system, enabling the file system to be resized, span across multiple physical disks, use arbitrary disk space, etc. LVM accumulates spaces taken from partitions or entire disks (called Physical Volumes) to form a logical container (called Volume Group), which is then divided into logical partitions (called Logical Volumes). The other key benefits of LVM include online resizing of volume groups and logical volumes, online data migration between logical volumes and between physical volumes, user-defined naming for volume groups and logical volumes, mirroring and striping across multiple physical disks, and snapshotting of logical volumes. Figure 14-1{.calibre5} depicts the LVM components.

::: c49 ::: width_ {.calibre13} :::

Figure 14-1 LVM Structure :::

As noted above, the LVM structure is made up of three key objects called physical volume, volume group, and logical volume. These objects are further virtually broken down into Physical Extents (PEs) and Logical Extents (LEs). The LVM components are explained in the following subsections.

Physical Volume

A Physical Volume (PV) is created when a block storage device such as a partition or an entire disk is initialized and brought under LVM control. This process constructs LVM data structures on the device, including a label on the second sector and metadata shortly thereafter. The label includes the UUID, size, and pointers to the locations of data and metadata areas. Given the criticality of metadata, LVM stores a copy of it at the end of the physical volume as well. The rest of the device space is available for use.

You can use an LVM command called pvs (physical volume scan or summary) to scan and list available physical volumes on server2:

{.image2}

The output shows one physical volume (PV) **devsda2 of size 9GB in rhel volume group (VG). Additional information displays the metadata format (Fmt) used, status of the physical volume under the Attr column (a for allocatable), and the amount of free space available on the physical volume (PFree).

Try running this command again with the -v flag to view more information about the physical volume.

[Volume]{#part0026_split_001.html#id_380 .calibre10} Group

A Volume Group (VG) is created when at least one physical volume is added to it. The space from all physical volumes in a volume group is aggregated to form one large pool of storage, which is then used to build logical volumes. The physical volumes added to a volume group may be of varying sizes. LVM writes volume group metadata on each physical volume that is added to it. The volume group metadata contains its name, date and time of creation, how it was created, the extent size used, a list of physical and logical volumes, a mapping of physical and logical extents, etc. A volume group can have a custom name assigned to it at the time of its creation. For example, it may be called vg01, vgora, or vgweb that identifies the type of information it is constructed to store. A copy of the volume group metadata is stored and maintained at two distinct locations on each physical volume within the volume group.

You can use an LVM command called vgs (volume group scan or summary) to scan and list available volume groups on server2:

{.image2}

The output shows one volume group (VG) rhel on server2 containing one physical volume (#PV). Additional information displays the number of logical volumes (#LV) and snapshots (#SN) in the volume group, status of the volume group under the Attr column (w for writeable, z for resizable, and n for normal), size of the volume group (VSize), and the amount of free space available in the volume group (VFree).

Try running this command again with the -v flag to view more information about the volume group.

Physical Extent

A physical volume is divided into several smaller logical pieces when it is added to a volume group. These logical pieces are known as Physical Extents (PE). An extent is the smallest allocatable unit of space in LVM. At the time of volume group creation, you can either define the size of the PE or leave it to the default value of 4MB. This implies that a 20GB physical volume would have approximately 5,000 PEs. Any physical volumes added to this volume group thereafter will use the same PE size.

You can use an LVM command called vgdisplay (volume group display) on server2 and grep for ‘PE Size’ to view the PE size used in the rhel volume group:

{.image2}

The output reveals the PE size used for the rhel VG.

[Logical]{#part0026_split_001.html#id_381 .calibre10} Volume

A volume group consists of a pool of storage taken from one or more physical volumes. This volume group space is used to create one or more Logical Volumes (LVs). A logical volume can be created or weeded out online, expanded or shrunk online, and can use space taken from one or multiple physical volumes inside the volume group.

The default naming convention used for logical volumes is lvol0, lvol1, lvol2, and so on; however, you may assign custom names to them. For example, a logical volume may be called system, undo, or webdata1 so as to establish the type of information it is constructed to store.

You can use an LVM command called lvs (logical volume scan or summary) to scan and list available logical volumes on server2:

{.image2}

The output shows two logical volumes root and swap in rhel volume group. Additional information displays the status of the logical volumes under the Attr column (w for writeable, i for inherited allocation policy, a for active, and o for open) and their sizes.

Try running this command again with the -v flag to view more information about the logical volumes.

[Logical]{#part0026_split_001.html#id_382 .calibre10} Extent

A logical volume is made up of Logical Extents (LE). Logical extents point to physical extents, and they may be random or contiguous. The larger a logical volume is, the more logical extents it will have. Logical extents are a set of physical extents allocated to the logical volume.

The PE and LE sizes are normally kept the same within a volume group; however, a logical extent can be smaller or larger than a physical extent. The default LE size is 4MB, which corresponds to the default PE size.

You can use an LVM command called lvdisplay (logical volume display) on server2 to view information about the root logical volume in the rhel volume group.

{.image2}

The output does not disclose the LE size; however, you can convert the LV size in MBs (8,000) and then divide the result by the Current LE count (2,047) to get the LE size (which comes close to 4MB).

[LVM]{#part0026_split_001.html#id_383 .calibre10} Operations and Commands

The LVM toolset offers a multitude of administrative commands to carry out various disk and volume management operations. These operations include creating and removing a physical volume, volume group, and logical volume; extending and reducing a volume group and logical volume; renaming a volume group and logical volume; and listing and displaying physical volume, volume group, and logical volume information.

Table 14-1{.calibre5} summarizes the common LVM tasks and the commands that are employed to accomplish them.

::: c49

Command Description Create and Remove Operations
pvcreate/pvremove Initializes/uninitializes a disk or partition for LVM use vgcreate/vgremove Creates/removes a volume group lvcreate/lvremove Creates/removes a logical volume Extend and Reduce Operations
vgextend/vgreduce Adds/removes a physical volume to/from a volume group lvextend/lvreduce Extends/reduces the size of a logical volume lvresize Resizes a logical volume. With the -r option, this command calls the resize2fs command and resizes the underlying file system as well. Applies to Ext2/Ext3/Ext4 file system types only. Rename Operations
vgrename Renames a volume group lvrename Renames a logical volume Command Description List and Display Operations
pvs/pvdisplay Lists/displays physical volume information vgs/vgdisplay Lists/displays volume group information lvs/lvdisplay Lists/displays logical volume information

[Table]{#part0026_split_001.html#id_741} 14-1 Common LVM Operations and Commands :::

All the tools accept the -v switch to support verbosity. Refer to the manual pages of the commands for usage and additional details.

As noted earlier, there are seven disks available on server2 for practice. Issue the lsblk command to confirm:

{.image2}

You will use the sdd and sde disks for LVM activities in the following exercises.

[Exercise]{#part0026_split_001.html#id_384 .calibre10} 14-1: Create a Physical Volume and Volume Group

This exercise should be done on server2 as user1 with sudo where required.

In this exercise, you will initialize one partition sdd1 (90MB) and one disk sde (250MB) for use in LVM. You will create a volume group called vgbook and add both physical volumes to it. You will use the PE size of 16MB and list and display the volume group and the physical volumes.

1[.]{.c19}Create a partition of size 90MB on sdd using the parted command and confirm. You need to label the disk first, as it is a new disk.

{.image2}

The print subcommand confirms the creation of the partition. It is the first partition on the disk.

2[.]{.c19}Set (set) the flag on the partition (1) to “lvm” using the parted command:

{.image2}

3[.]{.c19}Verify flag activation using the print subcommand with parted:

{.image2}

The flag is applied and enabled on the partition as indicated under the Flags column.

4[.]{.c19}Initialize the sdd1 partition and the sde disk using the pvcreate command. Note that there is no need to apply a disk label on sde with parted as LVM does not require it.

{.image2}

The command generated a verbose output. You now have two physical volumes available for use.

5[.]{.c19}Create vgbook volume group using the vgcreate command and add the two physical volumes to it. Use the -s option to specify the PE size in MBs.

{.image2}

The above command combines the two options with a single hyphen.

6[.]{.c19}List the volume group information:

{.image5} {.image5}

The total capacity available in the vgbook volume group is 320MB.

7.Display detailed information about the volume group and the physical volumes it contains:

{.image2}

The verbose output includes the physical volume attributes as well. There are a total of 20 PEs in the volume group (5 in sdd1 and 15 in sde), and each PE is 16MB in size. The collective size of all the physical volumes represents the total size of the volume group, which is 20x16 = 320MB.

8[.]{.c19}List the physical volume information:

{.image2}

The output shows the physical volumes in vgbook, along with their utilization status.

9[.]{.c19}Display detailed information about the physical volumes:

{.image2}

Once a partition or disk is initialized and added to a volume group, they are treated identically within the volume group. LVM does not prefer one over the other.

[Exercise]{#part0026_split_001.html#id_385 .calibre10} 14-2: Create Logical Volumes

This exercise should be done on server2 as user1 with sudo where required.

In this exercise, you will create two logical volumes, lvol0 and lvbook1, in the vgbook volume group. You will use 120MB for lvol0 and 192MB for lvbook1 from the available pool of space. You will display the details of the volume group and the logical volumes.

1[.]{.c19}Create a logical volume with the default name lvol0 using the lvcreate command. Use the -L option to specify the logical volume size, 120MB. You may use the -v, -vv, or -vvv option with the command for verbosity.

{.image2}

The size for the logical volume may be specified in units such as MBs, GBs, TBs, or as a count of LEs; however, MB is the default if no unit is specified (see the previous command). The size of a logical volume is always in multiples of the PE size. For instance, logical volumes created in vgbook with the PE size set at 16MB can be 16MB, 32MB, 48MB, 64MB, and so on. The output above indicates that the logical volume is 128MB (16x8), and not 120MB as specified.

2[.]{.c19}Create lvbook1 of size 192MB (16x12) using the lvcreate command. Use the -l switch to specify the size in logical extents and -n for the custom name. You may use -v for verbose information.

{.image2}

3[.]{.c19}List the logical volume information:

{.image2}

Both logical volumes are listed in the output with their attributes and sizes.

4[.]{.c19}Display detailed information about the volume group including the logical volumes and the physical volumes:

{.image2}

Alternatively, you can run the following to view only the logical volume details:

{.image2}

Review the attributes of the logical volumes as detailed above.

[Exercise]{#part0026_split_001.html#id_386 .calibre10} 14-3: Extend a Volume Group and a Logical Volume

This exercise should be done on server2 as user1 with sudo where required.

In this exercise, you will add another partition sdd2 of size 158MB to vgbook to increase the pool of allocatable space. You will initialize the new partition prior to adding it to the volume group. You will increase the size of lvbook1 to 336MB. You will display basic information for the physical volumes, volume group, and logical volume.

1[.]{.c19}Create a partition of size 158MB on sdd and set the flag to “lvm” using the parted command. Display the new partition to confirm the partition number, size, and flag.

{.image2}

2[.]{.c19}Initialize sdd2 using the pvcreate command:

{.image2}

3[.]{.c19}Extend vgbook by adding the new physical volume to it:

{.image2}

4[.]{.c19}List the volume group:

{.image2}

The output reflects the addition of a third physical volume to vgbook. The total capacity of the volume group has now increased to 464MB with 144MB free.

5[.]{.c19}Extend the size of lvbook1 to 340MB by adding 144MB using the lvextend command:

{.image2}

[EXAM TIP:]{.c56} Make sure the expansion of a logical volume does not affect the file system and the data it contains. More details in Chapter 15.

6[.]{.c19}Issue vgdisplay on vgbook with the -v switch for the updated details:

{.image2}

The output will show a lot of information about the volume group and the logical and physical volumes it contains. It will reflect the updates made in this exercise. In fact, each time a volume group or a logical volume is resized, vgdisplay will reflect those changes. The above output will display three physical volumes with the combined allocatable space grown to 464MB. The number of PEs will have increased to 29, with all of them allocated to logical volumes and 0 unused. The Logical Volume sections will display the updated information for the logical volumes. And at the very bottom, the three physical volumes will show with their device names, and total and available PEs in each.

7[.]{.c19}View a summary of the physical volumes:

{.image2}

8[.]{.c19}View a summary of the logical volumes:

{.image2}

This brings the exercise to an end.

[Exercise]{#part0026_split_001.html#id_387 .calibre10} 14-4: Rename, Reduce, Extend, and Remove Logical Volumes

This exercise should be done on server2 as user1 with sudo where required.

In this exercise, you will rename lvol0 to lvbook2. You will decrease the size of lvbook2 to 50MB using the lvreduce command and then add 32MB with the lvresize command. You will then remove both logical volumes. You will display the summary for the volume groups, logical volumes, and physical volumes.

1[.]{.c19}Rename lvol0 to lvbook2 using the lvrename command and confirm with lvs:

{.image2}

2[.]{.c19}Reduce the size of lvbook2 to 50MB with the lvreduce command. Specify the absolute desired size for the logical volume. Answer “Do you really want to reduce vgbook/lvbook2?” in the affirmative.

{.image2}

3[.]{.c19}Add 32MB to lvbook2 with the lvresize command:

{.image2}

4[.]{.c19}Use the pvs, lvs, vgs, and vgdisplay commands to view the updated allocation.

5[.]{.c19}Remove both lvbook1 and lvbook2 logical volumes using the lvremove command. Use the -f option to suppress the “Do you really want to remove active logical volume” message.

{.image2}

{.image} Removing a logical volume is a destructive task. You need to ensure that you perform a backup of any data in the target logical volume prior to deleting it. You will need to unmount the file system or disable swap in the logical volume. See Chapter 15{.calibre5} on how to unmount a file system and disable swap.

6[.]{.c19}Execute the vgdisplay command and grep for “Cur LV” to see the number of logical volumes currently available in vgbook. It should show 0, as you have removed both logical volumes.

{.image2}

This concludes the exercise.

[Exercise]{#part0026_split_001.html#id_388 .calibre10} 14-5: Reduce and Remove a Volume Group

This exercise should be done on server2 as user1 with sudo where required.

In this exercise, you will reduce vgbook by removing the sdd1 and sde physical volumes from it, and then remove the volume group. Confirm the deletion of the volume group and the logical volumes at the end.

1[.]{.c19}Remove sdd1 and sde physical volumes from vgbook by issuing the vgreduce command:

{.image2}

2[.]{.c19}Remove the volume group using the vgremove command. This will also remove the last physical volume, sdd2, from it.

{.image2}

{.image} You can also use the -f option with the vgremove command to force the volume group removal even if it contains any number of logical and physical volumes in it.

{.image} Remember to proceed with caution whenever you perform reduce and erase operations.

3[.]{.c19}Execute the vgs and lvs commands for confirmation:

{.image2}

This concludes the exercise.

[Exercise]{#part0026_split_001.html#id_389 .calibre10} 14-6: Uninitialize Physical Volumes

This exercise should be done on server2 as user1 with sudo where required.

In this exercise, you will uninitialize all three physical volumes—sdd1, sdd2, and sde—by deleting the LVM structural information from them. Use the pvs command for confirmation. Remove the partitions from the sdd disk and verify that all disks used in Exercises 14-1 to 14-5 are now in their original raw state.

1[.]{.c19}Remove the LVM structures from sdd1, sdd2, and sde using the pvremove command:

{.image2}

2[.]{.c19}Confirm the removal using the pvs command:

{.image2}

The partitions and the disk are now back to their raw state and can be repurposed.

3[.]{.c19}Remove the partitions from sdd using the parted command:

{.image2}

4[.]{.c19}Verify that all disks used in previous exercises have returned to their original raw state using the lsblk command:

{.image2}

This brings the exercise to an end.

We will recreate logical volumes in Chapter 15{.calibre5} and construct file system and swap structures in them.

[Stratis]{#part0026_split_001.html#id_390 .calibre10} Volume-Managing File System

RHEL 8 introduces a new simplified storage management solution called Stratis. Stratis capitalizes on three existing matured storage components: the device mapper (dm) kernel driver, the LVM solution, and the XFS file system. It implements the advanced features of these components to deliver file systems that are encapsulated within logical volumes. These logical volumes are created and expanded dynamically and transparently, hiding the underlying complexity. The Stratis solution delivers file systems that are referred to as volume-managing file systems. Stratis uses the thin provisioning technology as part of the solution.

{.image} File systems are explained in Chapter 15{.calibre5} “Local File Systems and Swap”.

The central idea surrounding the Stratis solution is a storage pool. A storage pool is created using at least one disk or partition, which is referred to as a blockdev. There can be a combination of the two in a single pool and more can be added as the space requirement grows. The total capacity of the pool is the aggregate of the spaces taken from all the block devices that are part of the pool. Within a pool, file systems can be created, all sharing the entire pool capacity.

{.image} LVM logical volumes can also be used as block devices in a Stratis pool.

Figure 14-2{.calibre5} provides a bird’s-eye view of the three major objects—pool, blockdev, and file system—used in Stratis.

::: c49 ::: width_ {.calibre13} :::

Figure 14-2 Stratis Structure :::

The diagram in Figure 14-2{.calibre5} shows a pool containing multiple disks and partitions. The pool capacity is the aggregate of all the block storage devices included in the pool, and this capacity is shared among all the file systems. Each Stratis file system appears to occupy the entire pool capacity exclusively; however, they are thinly provisioned. Their actual size grows as the amount of data stored in them increases. Stratis takes care of the dynamic expansion of the file systems and the underlying volumes as needed. As Stratis handles the creation, formatting, and expansion of the file systems, they must not be manually initialized or reconfigured.

Stratis Management Operations and Command

The primary command to manage Stratis is called stratis. This command has a set of subcommands available to perform management operations such as creating, viewing, renaming, and destroying pools and file systems, and expanding pools.

Table 14-2{.calibre5} summarizes the common Stratis subcommands that are employed to accomplish various management tasks.

::: c49

Command Description pool Administers storage pools. Subcommands are available to list, create, rename, expand, and destroy a pool. blockdev Lists block devices filesystem Administers file systems within storage pools. Subcommands are available to list, create, rename, and destroy a file system.

[Table]{#part0026_split_001.html#id_742} 14-2 Common Stratis Subcommands :::

Stratis runs as a service, so its operational state can be managed with the systemctl command. The stratis command interacts with the Stratis service to manage the pool and file systems dynamically.

For each pool added, Stratis creates a subdirectory under the /stratis directory matching the pool name. It then creates a symbolic link for each file system under that subdirectory to the actual device file located in the /dev directory.

Stratis file systems are not fixed-sized; however, pool space can be reserved to assure availability if multiple file systems share a pool.

[Exercise]{#part0026_split_001.html#id_391 .calibre10} 14-7: Install Software and Activate Stratis

This exercise should be done on server2 as user1 with sudo where required.

In this exercise, you will install the Stratis software packages, start the Stratis service, and mark it for autostart on subsequent system reboots.

1[.]{.c19}Install the packages stratisd and stratis-cli:

{.image2}

2[.]{.c19}Start the service and enable it to start automatically on future system reboots:

{.image2}

3[.]{.c19}Check the operational status of the service:

{.image2}

The relevant packages for the Stratis storage management solution are installed, and the Stratis service is started and activated. This concludes the exercise.

[Exercise]{#part0026_split_001.html#id_392 .calibre10} 14-8: Create and Confirm a Pool and File System

This exercise should be done on server2 as user1 with sudo where required.

In this exercise, you will create a Stratis pool and a file system in it. You will display information about the pool, file system, and device used.

1[.]{.c19}You allocated 2x1GB disks: sdg and sdh for Stratis exercises. Use the lsblk command to confirm their availability:

{.image2}

The 2x1GB disks are available and unused.

2[.]{.c19}Create a pool called bookpool using the sdg disk and verify the creation:

{.image2}

The specified pool bookpool is created. The second command output returns the basic information about the pool, including the number of physical devices used in the pool and their sizes, and the amount of in-use space in MiBs.

3[.]{.c19}Display the block device that is used to form the pool:

{.image2}

The pool bookpool has a single disk of size 1GiB and it is currently in use.

4[.]{.c19}Create a file system called bookfs in the bookpool and verify the creation:

{.image2}

The pool bookpool has a single file system bookfs of used size 546MiB. Its device file is **stratisbookpool/bookfs. The file system’s UUID is also displayed.

5[.]{.c19}Create a directory called /bookfs1 and mount the new file system on it:

{.image2}

6[.]{.c19}Check the pool usage:

{.image2}

Observe how the usage grew from 52MiB to 598MiB. This brings this exercise to an end.

[Exercise]{#part0026_split_001.html#id_393 .calibre10} 14-9: Expand and Rename a Pool and File System

This exercise should be done on server2 as user1 with sudo where required.

In this exercise, you will expand the Stratis pool bookpool (created in Exercise 14-8{.calibre5}) using the sdh disk. You will rename the pool and the file system it contains.

1[.]{.c19}Expand the bookpool pool by adding the sdh disk to it:

{.image2}

2[.]{.c19}Verify the new capacity of the pool:

{.image2}

The addition of another 1GB disk brings the total physical size to 2GiB.

3[.]{.c19}Change the name of the pool from bookpool to rhcsapool and verify:

{.image2}

The new name is depicted in the first column.

4[.]{.c19}Change the name of the file system from bookfs to rhcsafs, and verify:

{.image2}

The file system name is changed and it’s reflected in the output of the second command. The exercise is completed successfully.

[Exercise]{#part0026_split_001.html#id_394 .calibre10} 14-10: Destroy a File System and Pool

This exercise should be done on server2 as user1 with sudo where required.

In this exercise, you will destroy the Stratis file system and the pool that was created, expanded, and renamed in Exercises 14-8 and 14-9. You will verify the deletion with appropriate commands.

1[.]{.c19}The first step in the process is to unmount the file system rhcsafs1 from its mount point /bookfs1:

{.image2}

Unmounting a file system ensures that the file system is not busy.

2[.]{.c19}Remove the file system rhcsafs from the pool:

{.image2}

3[.]{.c19}Remove the pool rhcsapool from the system:

{.image2}

4[.]{.c19}Confirm the removal of the file system and the pool:

{.image2}

The above outputs confirm the removal of the file system and the pool.

5[.]{.c19}Verify that both sdg and sdh disks used in the previous Stratis exercises have returned to their original raw state using the lsblk command:

{.image2}

This concludes the exercise.

We will recreate Stratis file systems in Chapter 15{.calibre5} and add them for persistent mounting.

[Chapter]{#part0026_split_001.html#id_395 .calibre10} Summary

This chapter explicated two advanced storage management solutions: Logical Volume Manager and Stratis. The LVM solution has been around in RHEL for decades. The Stratis solution, on the other hand, is recently added.

We discovered how LVM works. We looked at various LVM objects and their relationship with one another. We explored LVM management commands and common options available with them. We performed a series of exercises to demonstrate the creation, expansion, renaming, reduction, and deletion of physical volumes, storage pools, and logical volumes.

The next advanced storage solution we looked at is called Stratis, which is a volume-managing file system. Stratis takes advantage of the underlying LVM functionality and the device mapper kernel driver to create and expand the XFS file system that it holds. Stratis dynamically expands the underlying LVM volume without the need for manual administrative intervention. We executed a couple of step-by-step exercises to explain the creation, growth, renaming, and removal of Stratis pools and file systems.

[Review]{#part0026_split_001.html#id_396 .calibre10} Questions

1[.]{.c19}The parted utility may be used to create LVM logical volumes. True or False?

2[.]{.c19}What are the two commands that you can use to reduce the number of logical extents from a logical volume?

3[.]{.c19}Stratis uses LVM as the underlying logical volume management solution. True or False?

4[.]{.c19}Provide the command to add physical volumes **devsdd1 and **devsdc to vg20 volume group.

5[.]{.c19}What are the two commands that you can use to add logical extents to a logical volume?

6[.]{.c19}Provide the command to create a volume group called vg20 on **devsdd disk with physical extent size 64MB.

7[.]{.c19}Name the three Stratis objects?

8[.]{.c19}Provide the command to remove vg20 along with logical and physical volumes it contains.

9[.]{.c19}What is the default size of a physical extent in LVM?

10[.]{.c23}What is the default name for the first logical volume in a volume group?

11[.]{.c23}What is one difference between the pvs and pvdisplay commands?

12[.]{.c23}When can a disk or partition be referred to as a physical volume?

13[.]{.c23}Provide the command to remove webvol logical volume from vg20 volume group.

14[.]{.c23}It is necessary to create file system structures in a logical volume before it can be used to store files in it. True or False?

15[.]{.c23}What would the command stratis pool create pool1 devsdg do?

16[.]{.c23}Physical and logical extents are typically of the same size. True or False?

17[.]{.c23}What is the purpose of the pvremove command?

18[.]{.c23}What would the command pvcreate devsdd do?

19[.]{.c23}A disk or partition can be added to a volume group without being initialized. True or False?

20[.]{.c23}What is the file system type that is created in a Stratis file system?

21[.]{.c23}Provide the command to create a logical volume called webvol of size equal to 100 logical extents in vg20 volume group.

22[.]{.c23}A volume group can be created without any physical volume in it. True or False?

23[.]{.c23}A single disk can be used by both parted and LVM solutions at the same time. True or False?

24[.]{.c23}Provide the command to add **devsdh to an existing pool called pool1.

25[.]{.c23}Provide the command to erase **devsdd1 physical volume from vg20 volume group.

26[.]{.c23}A partition can be used as an LVM object. True or False?

27[.]{.c23}Which command would you use to view the details of a volume group and its objects?

[Answers]{#part0026_split_001.html#id_397 .calibre10} to Review Questions

1[.]{.c19}False.

2[.]{.c19}The lvreduce and lvresize commands.

3[.]{.c19}True.

4[.]{.c19}vgextend vg20 devsdd1 devsdc

5[.]{.c19}The lvextend and lvresize commands.

6[.]{.c19}vgcreate -s 64 vg20 devsdd

7[.]{.c19}The three Stratis objects are pool, block device, and file system.

8[.]{.c19}vgremove -f vg20

9[.]{.c19}The default PE size is 4MB.

10[.]{.c23}lvol0 is the default name for the first logical volume created in a volume group.

11[.]{.c23}The pvs command lists basic information about physical volumes whereas the pvdisplay command shows the details.

12[.]{.c23}After the pvcreate command has been executed on it successfully.

13[.]{.c23}lvremove devvg20/webvol

14[.]{.c23}True.

15[.]{.c23}The command provided will create a Stratis pool called pool1 containing **devsdg device.

16[.]{.c23}True.

17[.]{.c23}The pvremove command is used to remove LVM information from a physical volume.

18[.]{.c23}The command provided will prepare the **devsdd disk for use in a volume group.

19[.]{.c23}False. A disk or partition must be initialized before it can be added to a volume group.

20[.]{.c23}XFS.

21[.]{.c23}lvcreate -l 100 -n webvol vg20

22[.]{.c23}False.

23[.]{.c23}True. A single disk can be shared between parted-created partitions and LVM.

24[.]{.c23}stratis pool add-data pool1 devsdh

25[.]{.c23}vgreduce vg20 devsdd1

26[.]{.c23}True.

27[.]{.c23}The vgdisplay command with the -v option.

[Do-]{#part0026_split_001.html#id_398 .calibre10}It-Yourself Challenge Labs

The following labs are useful to strengthen most of the concepts and topics learned in this chapter. It is expected that you perform the labs without external help. A step-by-step guide is not supplied, as the knowledge and skill required to implement the lab has already been disseminated in the chapter; however, hints to the relevant major topic(s) are included.

Add more storage to server2 if required.

[Lab]{#part0026_split_001.html#id_399 .calibre10} 14-1: Create Volume Group and Logical Volumes

As user1 with sudo on server2, initialize 1x250MB disk for use in LVM (use lsblk to identify available disks). Create volume group vg100 with PE size 16MB and add the physical volume. Create two logical volumes lvol0 and swapvol of sizes 100MB and 120MB. Use the vgs, pvs, lvs, and vgdisplay commands for verification. (Hint: Logical Volume Manager).

[Lab]{#part0026_split_001.html#id_400 .calibre10} 14-2: Expand Volume Group and Logical Volume

As user1 with sudo on server2, create a partition on an available 250MB disk and initialize it for use in LVM (use lsblk to identify available disks). Add the new physical volume to vg100. Expand the lvol0 logical volume to size 300MB. Use the vgs, pvs, lvs, and vgdisplay commands for verification. (Hint: Logical Volume Manager).

[Lab]{#part0026_split_001.html#id_401 .calibre10} 14-3: Reduce and Remove Logical Volumes

As user1 with sudo on server2, reduce the size of lvol0 logical volume to 80MB. Then erase both logical volumes swapvol and lvol0. Confirm the deletion with vgs, pvs, lvs, and vgdisplay commands. (Hint: Logical Volume Manager).

[Lab]{#part0026_split_001.html#id_402 .calibre10} 14-4: Remove Volume Group and Physical Volumes

As user1 with sudo on server2, remove the volume group and uninitialized the physical volumes. Confirm the deletion with vgs, pvs, lvs, and vgdisplay commands. Use the lsblk command and verify that the disks used for the LVM labs no longer show LVM information. (Hint: Logical Volume Manager).

[Lab]{#part0026_split_001.html#id_403 .calibre10} 14-5: Create Stratis Pool

As user1 with sudo on server2, check to see if Stratis software is installed and the Stratis service is enabled and started. Identify 2x1GB disks with the lsblk command and ensure they are not in use. Create pool strpool on one of the 1GB disks and verify the pool and the block device with the stratis command. (Hint: Stratis Volume-Managing File System).

[Lab]{#part0026_split_001.html#id_404 .calibre10} 14-6: Expand and Destroy Stratis Pool

As user1 with sudo on server2, use the other 1GB disk and expand strpool using the stratis command. Verify the expansion. Finally, remove the entire pool and confirm the deletion. Use the lsblk command and verify that the disks used for the Stratis labs no longer show Stratis information. (Hint: Stratis Volume-Managing File System).

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