Logical Volume Management

Notes

• If you make changes on the fly, and are unable to mount volumes, try "systemctl daemon-reload" first.

Create Mirrored Volume

Purpose

To mirror two 4TB disks.

Steps

[root@natasha ~]# pvcreate /dev/sd[b-c]
  Physical volume "/dev/sdb" successfully created.
  Physical volume "/dev/sdc" successfully created.

[root@natasha ~]# vgcreate DATA /dev/sd[b-c]
  Volume group "DATA" successfully created

[root@natasha ~]# lvcreate -m1 -L 3.63T -n mirror1 DATA
  Rounding up size to full physical extent 3.63 TiB
  Logical volume "mirror1" created.

[root@natasha ~]# mkfs.ext4 /dev/mapper/DATA-mirror1
mke2fs 1.44.3 (10-July-2018)
Creating filesystem with 974420992 4k blocks and 243605504 inodes
Filesystem UUID: 4c050c23-6e5b-4747-9ec5-39ea112b39ba
Superblock backups stored on blocks: 
	32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
	4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968, 
	102400000, 214990848, 512000000, 550731776, 644972544

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (262144 blocks): done
Writing superblocks and filesystem accounting information: done  

[root@natasha ~]# mkdir /data

[root@natasha ~]# mount /dev/mapper/DATA-mirror1 /data/

[root@natasha ~]# df -h
Filesystem                Size  Used Avail Use% Mounted on
devtmpfs                  3.8G     0  3.8G   0% /dev
tmpfs                     3.8G     0  3.8G   0% /dev/shm
tmpfs                     3.8G  8.8M  3.8G   1% /run
tmpfs                     3.8G     0  3.8G   0% /sys/fs/cgroup
/dev/mapper/OS-root       103G  2.7G  100G   3% /
/dev/sda2                 976M  183M  727M  21% /boot
/dev/sda1                 599M  6.8M  593M   2% /boot/efi
tmpfs                     770M     0  770M   0% /run/user/0
/dev/mapper/DATA-mirror1  3.6T   89M  3.4T   1% /data

Troubleshooting

The following fields are helpful for monitoring RAID status. This can be pulled using

lvs -o ?

• raid_mismatch_count - For RAID, number of mismatches found or repaired.
• raid_sync_action - For RAID, the current synchronization action being performed.
• raid_write_behind - For RAID1, the number of outstanding writes allowed to writemostly devices.
• raid_min_recovery_rate - For RAID1, the minimum recovery I/O load in kiB/sec/disk.
• raid_max_recovery_rate - For RAID1, the maximum recovery I/O load in kiB/sec/disk.

i.e.

[root@natasha ~]# lvs -o raid_mismatch_count
  Mismatches
           0

Create Cache

Working off the mirror LVM created previsouly, I needed to increase performance on these SMR drives. I had an NVME drive connected via USB 3.0 that would work for now.

Read Cache

pvcreate /dev/sda1
vgextend DATA /dev/sda1
lvcreate -n cache-write -L 50GB DATA /dev/sda1
lvcreate -n cache-read -L 100GB DATA /dev/sda1
lvconvert --type cache --cachevol cache-read --chunksize=256 DATA/mirror1

[root@natasha ~]# lvs -o cache_used_blocks,cache_read_hits,cache_read_misses
  CacheUsedBlocks  CacheReadHits    CacheReadMisses 
                                                    
               162               89              205

Fix excluded by filter

[root@natasha ~]# wipefs -a /dev/sdb
/dev/sdb: 8 bytes were erased at offset 0x00000200 (gpt): 45 46 49 20 50 41 52 54
/dev/sdb: 8 bytes were erased at offset 0x3a3817d5e00 (gpt): 45 46 49 20 50 41 52 54
/dev/sdb: 2 bytes were erased at offset 0x000001fe (PMBR): 55 aa
/dev/sdb: calling ioctl to re-read partition table: Success

Grow logical volume

Purpose

A couple small servers I had built using the vmware defaults started to run out of space, and everytime this happens I fail to record the steps and have to look up a refresher. This time I will record it.

Steps

NOTE: The following uses defaults. If you need to look up specific information on your system, use vgdisplay and lvdisplay.

• Create a new partition on the disk

fdisk /dev/sda
Welcome to fdisk (util-linux 2.23.2).

Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): p

Disk /dev/sda: 21.5 GB, 21474836480 bytes, 41943040 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000606ed

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048     1026047      512000   83  Linux
/dev/sda2         1026048    20971519     9972736   8e  Linux LVM

Command (m for help): n
Partition type:
   p   primary (2 primary, 0 extended, 2 free)
   e   extended
Select (default p):
Using default response p
Partition number (3,4, default 3):
First sector (20971520-41943039, default 20971520):
Using default value 20971520
Last sector, +sectors or +size{K,M,G} (20971520-41943039, default 41943039):
Using default value 41943039
Partition 3 of type Linux and of size 10 GiB is set

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.

• Run partprobe so kernel knows of new partition.
• Add the partition as a physical parition for LVM

pvcreate /dev/sda3

• Add the new physical volume to the volume group

vgextend centos /dev/sda3

• Extend the logical volume

lvextend /dev/centos/root /dev/sda3

VMWare Specific

To detect a resized disk running on VMWare, you need to scan the scsi controller before expanding the volume.

echo 1 > /sys/class/scsi_device/0\:0\:0\:0/device/rescan