Create & Manage Striped Logical Volume Linux [Step-by-Step]

Striped Logical Volumes - Overview

When we create a Linear logical volume, the LVM assigns a range of physical extents to an area of a logical volume in order. It could be a single disk or more. However, we can control the way the data is written to the physical volumes by creating a striped logical volume.

The benefits of using LVM Striping features are;

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  • Striping enhances performance of disks by increasing I/O. For large sequential reads and writes, this can improve the efficiency of the data I/O.
  • With striping, I/O can be done in parallel. Reduces Disk IO Wait by writing data over multiple disks simultaneously.
  • We can manage the disk space issues by creating striping over multiple disks. This can help to  reduce the Disk fill-up issue.
NOTE:

Striped logical volume or striped RAID is not recommended. The disadvantage of disk striping is low resiliency. Striped volumes do not offer fault tolerance. If a disk in a striped volume fails, the data in the entire volume is lost. However, a striped volume can be mirrored to provide data redundancy.

Lab Environment and Requirements

Root access to a Linux System of any distribution with two or more number of Additional Disks attached are required. We have used 4x10GB of additional disks which will use for different sections during the course of this tutorial for testing.

Before learning the Striped Volumes, We need to have a basic understanding of the Logical Volume Manager and knowledge in creating basic linear logical volumes. Please refer the following articles for more information about LVM :

Beginners guide to how LVM works in Linux (architecture)
Manage Logical Volume in Linux – One STOP Solution

Note: Change the device names as it is in your system. You can change the Volume group name or Logical volume names as per your understanding

 

Create Striped Logical Volumes

Once you have added the disks to your Linux server, you can proceed with the following steps to create striped logical volumes:

 

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Step 1. Create Device Partition

In the initial step let us create disk partitions. We are using only 2x10GB drives here.

We can use parted or fdisk for partitioning. In the example, we have used parted utility. fdisk to create disk partitions:

[root@lvm-setup ~]# parted --script /dev/sdb "mklabel gpt"
[root@lvm-setup ~]# parted --script /dev/sdb "mkpart 'LVM2' 0% 100%"
[root@lvm-setup ~]# parted --script /dev/sdb "set 1 lvm on"


[root@lvm-setup ~]# parted --script /dev/sdc "mklabel gpt"
[root@lvm-setup ~]# parted --script /dev/sdc "mkpart 'LVM2' 0% 100%"
[root@lvm-setup ~]# parted --script /dev/sdc "set 1 lvm on"

 

Step 2. Create Physical Volume

Now let's create the Physical volumes using partitions /dev/sdb1 and /dev/sdc1

[root@lvm-setup ~]# pvcreate /dev/sdb1 /dev/sdc1

Sample Output:

Create & Manage Striped Logical Volumes Linux [Step-by-Step]

 

Step 3. Create Volume Group

In the example, we have created a VG named volgroup_striped from the PVs /dev/sdb1 and /dev/sdc1. We will be using this VG volgroup_striped across these tutorials.

[root@lvm-setup ~]# vgcreate volgroup_striped /dev/sdb1 /dev/sdc1
  Volume group "volgroup_striped" successfully created

 

Step 4. Creating a Striped Logical Volume

Here is an example to create a striped volume  lv_striped using VG volgroup_striped :

[root@lvm-setup ~]# lvcreate -i2 -I64 -L2G -n lv_striped volgroup_striped
  Logical volume "lv_striped" created.

From the above example

  • -i2  means the number of stripes that need to be created.   Here we are using 2 disks, so 2 stripes.
  • -I64 means the stripesize in KB. The stripe size used was 64 KB (the default).
  • -L2G is the size of the Logical volume. We have used 2GB of size.
  • -n for the name of the volume.

 

Let's check the created striped volume using lvs command. From the output, we can confirm the volume is created using /dev/sdb1 and /dev/sdc1

[root@lvm-setup ~]# lvs -a -o +devices -o +segtype
  LV         VG               Attr       LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices                   Type   
  lv_striped volgroup_striped -wi-a----- 2.00g                                                     /dev/sdb1(0),/dev/sdc1(0) striped

 

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Step 5. Create filesystem and mount the striped volume

Here we are creating  ext4 filesystem and mount the striped volume. Please refer for more information: Create file systems and mount the Logical Volumes

[root@lvm-setup ~]# mkfs.ext4 /dev/volgroup_striped/lv_striped

Sample Output:

Create & Manage Striped Logical Volumes Linux [Step-by-Step]

Mount this Logical Volume temporarily to /mnt. You can use any mount points to mount it.

[root@lvm-setup ~]# mount /dev/volgroup_striped/lv_striped /mnt

[root@lvm-setup ~]# df -h /mnt
Filesystem                               Size  Used Avail Use% Mounted on
/dev/mapper/volgroup_striped-lv_striped  2.0G  6.0M  1.8G   1% /mnt

 

Step 6. Create some test files under striped volume

Now you can go ahead and access your striped logical volume and store data. Here just for demonstration we have created some files and directories on our striped LVM.

[root@lvm-setup ~]# cd /mnt

[root@lvm-setup mnt]# touch testfile.txt

[root@lvm-setup mnt]# ls -al
total 16
drwx------ 2 root root 16384 Aug 11 11:44 lost+found
-rw-r--r-- 1 root root     0 Aug 11 11:49 testfile.txt

[root@lvm-setup mnt]# ls -l
total 16
drwx------ 2 root root 16384 Aug 13 10:51 lost+found
-rw-r--r-- 1 root root     0 Aug 13 10:52 teststripe.txt

 

Convert existing Striped Logical Volume to a Linear Logical Volume

There is no direct command to convert striped LV to Linear. First, we need to convert the striped into a mirrored logical volume and convert the mirrored volume back to linear. Let us discuss this in the following steps.

 

Step 1. Add a new drive to the Volume Group

As discussed, we need to create the partitions for the new drive and create PV. When you are adding a new drive, you need to make sure that the new drive has enough space to hold the data from the striped volumes. Then we need to add the new drive to our existing VG volgroup_striped

In the example, I am adding a new drive /dev/sdd1 to the VG volgroup_striped

[root@lvm-setup ~]# parted --script /dev/sdd "mklabel gpt"
[root@lvm-setup ~]# parted --script /dev/sdd "mkpart 'LVM2' 0% 100%"
[root@lvm-setup ~]# parted --script /dev/sdd "set 1 lvm on"

[root@lvm-setup ~]# pvcreate /dev/sdd1
  Physical volume "/dev/sdd1" successfully created.

[root@lvm-setup ~]# vgextend volgroup_striped /dev/sdd1
  Volume group "volgroup_striped" successfully extended

 

Step 2. Convert striped volume into mirrored logical volume

Let us convert the striped volume lv_striped to mirrored volume. The mirror will be created under the new disk /dev/sdd1.

When you are using huge size disks the process will take hours to complete. You need to run these commands in the screen. In the below command with option --mirrorlog core. I have kept the logs in the system memory. We can also add another physical device to the Volume group so that the logs can be kept on the disk and then try to run the lvconvert command. -m1 is used for one mirror.

[root@lvm-setup ~]# lvconvert -m1 --type mirror --corelog /dev/volgroup_striped/lv_striped /dev/sdd1
  Logical volume volgroup_striped/lv_striped being converted.
  volgroup_striped/lv_striped: Converted: 0.00%
  volgroup_striped/lv_striped: Converted: 13.67%
  volgroup_striped/lv_striped: Converted: 27.34%
  volgroup_striped/lv_striped: Converted: 41.41%
  volgroup_striped/lv_striped: Converted: 54.10%
  volgroup_striped/lv_striped: Converted: 66.60%
  volgroup_striped/lv_striped: Converted: 79.69%
  volgroup_striped/lv_striped: Converted: 92.97%
  volgroup_striped/lv_striped: Converted: 100.00%

The below output shows that the striped volume is also mirrored.

[root@lvm-setup ~]# lvs -a -o +segtype
  LV                    VG               Attr       LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert Type   
  lv_striped            volgroup_striped mwi-a-m--- 2.00g                                    100.00           mirror 
  [lv_striped_mimage_0] volgroup_striped iwi-aom--- 2.00g                                                     striped
  [lv_striped_mimage_1] volgroup_striped iwi-aom--- 2.00g                                                     linear

 

Step 3. Convert mirrored volume into Linear volume

Here we are converting the mirrored volume into a Linear volume by removing the PVs /dev/sdb1 and /dev/sdc1. If you remember, these two physical volumes are used to create a striped volume. So, we are removing those as we have a mirrored copy in /dev/sdd1. -m0 is used for zero mirrors.

[root@lvm-setup ~]# lvconvert -m 0 /dev/volgroup_striped/lv_striped /dev/sdb1 /dev/sdc1
  Logical volume volgroup_striped/lv_striped converted.

We are safely converted our striped logical volume to linear. The below output shows the volume is now existing only in /dev/sdd1 as linear.

[root@lvm-setup ~]# lvs -a -o +devices -o +segtype
  LV         VG               Attr       LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices      Type  
  lv_striped volgroup_striped -wi-ao---- 2.00g                                                     /dev/sdd1(0) linear

We can also confirm the data we stored under the mounted volume. Which will remain safe.

 

Convert existing Linear Logical Volume to a Striped Logical Volumes

As same as in the above section, there is no direct command to convert Linear LV to Striped Logical Volume. We need to convert the Linear LV to mirrored LV with stripes(Mirroring using 2 drives). Then we can convert it into Striped LV by removing the existing device (One drive mirror).

Let us find the physical volume(s) that hold a logical volume using lvs command as below. In the example, the linear logical volume is under PV /dev/sdd1.

[root@lvm-setup ~]# lvs -a -o +devices -o +segtype
  LV         VG               Attr       LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices      Type  
  lv_striped volgroup_striped -wi-ao---- 2.00g                                                     /dev/sdd1(0) linear

 

Step 1: Attach additional disks.

In the example we already have 2 additional PV /dev/sdb1 and /dev/sdc1. If you do not have the ones; need to re-add the drives. Refer Managing LVM Physical Volumes

Also, the PVs are already added to the VG volgroup_striped. If not, need to add those Add Physical Volumes to a Volume Group

[root@lvm-setup ~]# pvs

Sample Output:

Create & Manage Striped Logical Volumes Linux [Step-by-Step]

 

Step 2. Create a mirror of the current data

Let us create a mirror of the current data /dev/volgroup_striped/lv_striped to the additional available devices /dev/sdb1 and /dev/sdc1. In the below example we have created a mirror And make it stripe (--stripes <number of disks>).

Depending on the size of the conversion this will take time. Do this in a screen if the size of the data is large.

[root@lvm-setup ~]# lvconvert --mirrors 1 /dev/volgroup_striped/lv_striped --mirrorlog core --type mirror --stripes 2
  Using default stripesize 64.00 KiB.
  Logical volume volgroup_striped/lv_striped being converted.
  volgroup_striped/lv_striped: Converted: 0.00%
  volgroup_striped/lv_striped: Converted: 12.30%
  volgroup_striped/lv_striped: Converted: 24.02%
  volgroup_striped/lv_striped: Converted: 36.13%
  volgroup_striped/lv_striped: Converted: 48.63%
  volgroup_striped/lv_striped: Converted: 60.35%
  volgroup_striped/lv_striped: Converted: 72.46%
  volgroup_striped/lv_striped: Converted: 84.57%
  volgroup_striped/lv_striped: Converted: 96.48%
  volgroup_striped/lv_striped: Converted: 100.00%

Once it's converted, you will see the below results. Where the the disk  /dev/sdd1 is mirrored by stripes /dev/sdb1 and /dev/sdc1.

[root@lvm-setup ~]# lvs -a -o +devices -o +segtype
  LV                    VG               Attr       LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices                                       Type   
  lv_striped            volgroup_striped mwi-aom--- 2.00g                                    100.00           lv_striped_mimage_0(0),lv_striped_mimage_1(0) mirror 
  [lv_striped_mimage_0] volgroup_striped iwi-aom--- 2.00g                                                     /dev/sdd1(0)                                  linear 
  [lv_striped_mimage_1] volgroup_striped iwi-aom--- 2.00g                                                     /dev/sdb1(0),/dev/sdc1(0)                     striped

 

Step 3. Remove the mirror

In this step let us remove the mirror. -m0 will set the volume with No mirror. In the example, we are removing the original drive /dev/sdd1.

[root@lvm-setup ~]# lvconvert -m0 /dev/volgroup_striped/lv_striped /dev/sdd1
  Logical volume volgroup_striped/lv_striped converted.

Now the volume has been converted into striped volume with stripes /dev/sdb1 and /dev/sdc1.

[root@lvm-setup ~]# lvs -a -o +devices -o +segtype
  LV         VG               Attr       LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices                   Type   
  lv_striped volgroup_striped -wi-ao---- 2.00g                                                     /dev/sdb1(0),/dev/sdc1(0) striped

 

Extend Striped volume by adding new Disks

In order to increase the size of a striped logical volume, there must be enough free space on the underlying physical volumes that make up the volume group to support the stripe. For example, if you have a two-way stripe that uses up an entire volume group, adding a single physical volume to the volume group will not enable you to extend the stripe. Instead, you must add at least two physical volumes to the volume group.

In the below example the striped volume is using /dev/sdb1 and /dev/sdc1. We can extend the volume up to 20GB. However, if you try to extend up to the VG size 29.99G, the volume group will not enable you to extend the stripe. Instead it will use a single additional disk to act as a linear volume.

The below commands list the current status of the striped logical volume.

# LV status
[root@lvm-setup ~]# lvs -a -o +devices -o +segtype
  LV         VG               Attr       LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices                   Type   
  lv_striped volgroup_striped -wi-a----- 2.00g                                                     /dev/sdb1(0),/dev/sdc1(0) striped

# PV status
[root@lvm-setup ~]# pvs
PV VG Fmt Attr PSize PFree 
/dev/sdb1 volgroup_striped lvm2 a-- <10.00g <9.00g
/dev/sdc1 volgroup_striped lvm2 a-- <10.00g <9.00g
/dev/sdd1 volgroup_striped lvm2 a-- <10.00g <10.00g

# VG status 
[root@lvm-setup ~]# vgs
VG #PV #LV #SN Attr VSize VFree 
volgroup_striped 3 1 0 wz--n- <29.99g <27.99g

When we try to extend the striped volume to 29GB, you will get the below error;

[root@lvm-setup ~]# lvextend /dev/volgroup_striped/lv_striped -L 29G
  Using stripesize of last segment 64.00 KiB
  Insufficient suitable allocatable extents for logical volume lv_striped: 2306 more required

However, it is possible to extend the volume anyway if it does not matter that the extension is not striped, which may result in an uneven performance. The following example extends the existing striped logical volume to use the remaining free space in VG volgroup_striped after the initial lvextend command fails.

We are not trying this command as we are extending striped volume with another additional disk in the next step.

[root@lvm-setup ~]#  lvextend -iL -l+100%FREE vg/stripe1

 

Step 1: Add Additional disks to Volume Group

As discussed, we have a two-way stripe that uses up an entire volume group. We must add at least two physical volumes to the volume group to extend with stripes.

In the example we are extending the VG with another disk /dev/sde1 . Now we have a total of 4x10GB drives. Refer the article for more information about partitioning and extending volume groups.

[root@lvm-setup ~]# pvcreate /dev/sde1
  Physical volume "/dev/sde1" successfully created.

[root@lvm-setup ~]# vgextend volgroup_striped /dev/sde1
  Volume group "volgroup_striped" successfully extended

[root@lvm-setup ~]# pvs
  PV         VG               Fmt  Attr PSize   PFree  
  /dev/sdb1  volgroup_striped lvm2 a--  <10.00g  <9.00g
  /dev/sdc1  volgroup_striped lvm2 a--  <10.00g  <9.00g
  /dev/sdd1  volgroup_striped lvm2 a--  <10.00g <10.00g
  /dev/sde1  volgroup_striped lvm2 a--  <10.00g <10.00g

Once the VG is extended we have 4 PVs with around 40GB of free space.

[root@lvm-setup ~]# vgs
  VG               #PV #LV #SN Attr   VSize  VFree 
  volgroup_striped   4   1   0 wz--n- 39.98g 37.98g

 

Step 2 : Extend the Striped volume with additional disks

Now, if we try to extend the volume with the available 39GB space, it will extend without any errors.

[root@lvm-setup ~]# lvextend /dev/volgroup_striped/lv_striped -L 39G
  Using stripesize of last segment 64.00 KiB
  Size of logical volume volgroup_striped/lv_striped changed from 2.00 GiB (512 extents) to 39.00 GiB (9984 extents).
  Logical volume volgroup_striped/lv_striped successfully resized.

We can confirm the striped volumes in the below lvs output. It has created two-way striping with 2 PVs each.

[root@lvm-setup ~]# lvs -a -o +devices -o +segtype
  LV         VG               Attr       LSize  Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices                   Type   
  lv_striped volgroup_striped -wi-a----- 39.00g                                                     /dev/sdb1(0),/dev/sdc1(0) striped
  lv_striped volgroup_striped -wi-a----- 39.00g                                                     /dev/sdd1(0),/dev/sde1(0) striped

 

Step 2: Extend the filesystem

Once the Logical volume is extended, we also need to extend the filesystem. Before extending the filesystem, it will show up only existing disk space.

[root@lvm-setup ~]# df -h /mnt
Filesystem                               Size  Used Avail Use% Mounted on
/dev/mapper/volgroup_striped-lv_striped  2.0G  6.0M  1.8G   1% /mnt

To extend the ext filesystems use resize2fs. Once the resize2fs is finished, the mounted filesystem will show the proper size. For more info refer : Create file systems and mount the Logical Volumes

[root@lvm-setup ~]# resize2fs /dev/mapper/volgroup_striped-lv_striped
resize2fs 1.45.6 (20-Mar-2020)
Filesystem at /dev/mapper/volgroup_striped-lv_striped is mounted on /mnt; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 5
The filesystem on /dev/mapper/volgroup_striped-lv_striped is now 10223616 (4k) blocks long.

[root@lvm-setup ~]# df -h /mnt
Filesystem                               Size  Used Avail Use% Mounted on
/dev/mapper/volgroup_striped-lv_striped   39G   12M   37G   1% /mnt

 

Summary

In this article we covered following topics:

  • How to create striped logical volume
  • How to convert striped to linear logical volume and vice versa
  • How to extend the size of existing striped logical volume

 

References

CREATING A STRIPED LOGICAL VOLUME
Setting up LVM on three SCSI disks with striping

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