适用场景

看到B站技术部门的文章，是关于如何在k8s集群部署Elastic Search和Click House等IO密集型数据库应用的。
因为要充分利用NvME SSD盘的IOPS，所有数据库应用都直接调用本地SSD盘做为stateful application的 Persistent Volumes。为了可用动态的分配大小不一的本地磁盘空间给k8s创建的pods使用，最合适的本地磁盘系统应该为LVM。
最近两天我在自己的虚拟集群里实现了lvm类型的storage class，并测试了调用此storagecalss的PVC， 确认可用正常生成需要的PV并bound给到pods使用。

再说一次，LVM 类型的StorageClass 适用于有状态的应用直接调用本地磁盘来确保高IOPS的使用场景（如数据库应用）

知识储备建议

本文将使用到如下知识，建议阅读者有如下知识储备：

1. LVM相关概念如 PV VG LV， fdisk命令的使用
2. CSI相关概念，Helm，chart/release
3. k8s存储相关PV PVC SC（StorageClass）

实现原理

Worker node安装lvm，并创建相应vg；Master CP安装CSI插件并生成相应StorageClass。 当API server 检测到PVC时，自动通过StorageClass生成lvm的PV。
（原谅我懒得画个图）

步骤分解并注释

Worker node 实现lvm存储

给虚拟机添加新磁盘

因为我的集群是个vmware workstaion的集群，首先需要给worker node的虚拟机增加第二块磁盘，然后

root@slave2:/home/bill# lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
sda      8:0    0   20G  0 disk 
├─sda1   8:1    0   19G  0 part /
├─sda2   8:2    0    1K  0 part 
└─sda5   8:5    0  975M  0 part 
sr0     11:0    1  631M  0 rom  
# lsblk是list block设备的命令，发现还是只有一个名叫 sda 的磁盘， 并没有找到第二块新增的盘。我新增的SCSI格式磁盘，理论上不需要重启即可挂载
root@slave2:/home/bill# echo "- - -" | sudo tee /sys/class/scsi_host/host*/scan
- - -
# Chatgpt告诉我这个命令可用强制刷新
root@slave2:/home/bill# lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
sda      8:0    0   20G  0 disk 
├─sda1   8:1    0   19G  0 part /
├─sda2   8:2    0    1K  0 part 
└─sda5   8:5    0  975M  0 part 
sdb      8:16   0   20G  0 disk 
sr0     11:0    1  631M  0 rom  
# 好了，有了第二块 sdb 磁盘了
root@slave2:/home/bill# sudo fdisk /dev/sdb
# 自从上云后，很少管理裸金属服务器了，很多命令如fdisk iptables 很久不用要生疏了。 fdisk是linux常用的用来对磁盘进行分区管理并格式化的工具。
Welcome to fdisk (util-linux 2.38.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Device does not contain a recognized partition table.
Created a new DOS (MBR) disklabel with disk identifier 0x907350bf.

Command (m for help): h
h: unknown command
# 别学我，习惯用h， 人家分明说”m for help“
# 你知道什么是partition 么 ？ 这个是要进行fdisk操作的最基础概念，需要去google下如果你不知道的话。
Command (m for help): m

Help:

  DOS (MBR)
   a   toggle a bootable flag
   b   edit nested BSD disklabel
   c   toggle the dos compatibility flag

  Generic
   d   delete a partition #慎用
   F   list free unpartitioned space
   l   list known partition types
   n   add a new partition #新增分区，必用
   p   print the partition table #常用，用来显示当前磁盘和分区情况
   t   change a partition type
   v   verify the partition table
   i   print information about a partition

  Misc
   m   print this menu
   u   change display/entry units
   x   extra functionality (experts only)

  Script
   I   load disk layout from sfdisk script file
   O   dump disk layout to sfdisk script file

  Save & Exit
   w   write table to disk and exit #修改了磁盘分区partition后一定要用w，只有这样才可用保存你的变更
   q   quit without saving changes # 最后使用

  Create a new label
   g   create a new empty GPT partition table
   G   create a new empty SGI (IRIX) partition table
   o   create a new empty MBR (DOS) partition table
   s   create a new empty Sun partition table


Command (m for help): p #打印看下，fdisk是否检测到了新增磁盘

Disk /dev/sdb: 20 GiB, 21474836480 bytes, 41943040 sectors
Disk model: VMware Virtual S
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x907350bf
#检测到/dev/sdb了，你最好有扇区这么个概念，不过SSD盘已经没有扇区了，fdisk延用了而已。
Command (m for help): n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (1-4, default 1): 
First sector (2048-41943039, default 2048): 
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-41943039, default 41943039): 

Created a new partition 1 of type 'Linux' and of size 20 GiB.

Command (m for help): p
Disk /dev/sdb: 20 GiB, 21474836480 bytes, 41943040 sectors
Disk model: VMware Virtual S
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x907350bf

Device     Boot Start      End  Sectors Size Id Type
/dev/sdb1        2048 41943039 41940992  20G 83 Linux

Command (m for help): m

Help:

  DOS (MBR)
   a   toggle a bootable flag
   b   edit nested BSD disklabel
   c   toggle the dos compatibility flag

  Generic
   d   delete a partition
   F   list free unpartitioned space
   l   list known partition types
   n   add a new partition
   p   print the partition table
   t   change a partition type
   v   verify the partition table
   i   print information about a partition

  Misc
   m   print this menu
   u   change display/entry units
   x   extra functionality (experts only)

  Script
   I   load disk layout from sfdisk script file
   O   dump disk layout to sfdisk script file

  Save & Exit
   w   write table to disk and exit
   q   quit without saving changes

  Create a new label
   g   create a new empty GPT partition table
   G   create a new empty SGI (IRIX) partition table
   o   create a new empty MBR (DOS) partition table
   s   create a new empty Sun partition table


Command (m for help): d
Selected partition 1
Partition 1 has been deleted.

Command (m for help): p
Disk /dev/sdb: 20 GiB, 21474836480 bytes, 41943040 sectors
Disk model: VMware Virtual S
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x907350bf

Command (m for help): n # n 用来新增一个分区partition，因为这时候磁盘还是裸的，即没有分区，更没有对分区进行格式化（如xfs，ext4）以便系统可用拿来存放数据文件
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p # n 命令下的子选项， p表示primary partition主分区，而不是e extended 扩展分区
Partition number (1-4, default 1): #你就空着吧，太细节了 不用管
First sector (2048-41943039, default 2048): #你就空着吧，太细节了 不用管
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-41943039, default 41943039): #你就空着吧，太细节了 不用管，这个就是扇区了，其实可用精细的调整一些物理磁盘的东西的，不过我们的主要目标是k8s管理lvm本地磁盘，所以都略了。

Created a new partition 1 of type 'Linux' and of size 20 GiB.
# 给创建了一个type 为 Linux 的分区
Command (m for help): t #t， 我们需要的是lvm type的分区，所以用 t 来trans
Selected partition 1 #只有1个partition /dev/sdb1
Hex code or alias (type L to list all): L # 我们来用L看一下有多少分区类型可选

00 Empty            27 Hidden NTFS Win  82 Linux swap / So  c1 DRDOS/sec (FAT-
01 FAT12            39 Plan 9           83 Linux            c4 DRDOS/sec (FAT-
02 XENIX root       3c PartitionMagic   84 OS/2 hidden or   c6 DRDOS/sec (FAT-
03 XENIX usr        40 Venix 80286      85 Linux extended   c7 Syrinx         
04 FAT16 <32M       41 PPC PReP Boot    86 NTFS volume set  da Non-FS data    
05 Extended         42 SFS              87 NTFS volume set  db CP/M / CTOS / .
06 FAT16            4d QNX4.x           88 Linux plaintext  de Dell Utility   
07 HPFS/NTFS/exFAT  4e QNX4.x 2nd part  8e Linux LVM        df BootIt         
08 AIX              4f QNX4.x 3rd part  93 Amoeba           e1 DOS access     
09 AIX bootable     50 OnTrack DM       94 Amoeba BBT       e3 DOS R/O        
0a OS/2 Boot Manag  51 OnTrack DM6 Aux  9f BSD/OS           e4 SpeedStor      
0b W95 FAT32        52 CP/M             a0 IBM Thinkpad hi  ea Linux extended 
0c W95 FAT32 (LBA)  53 OnTrack DM6 Aux  a5 FreeBSD          eb BeOS fs        
0e W95 FAT16 (LBA)  54 OnTrackDM6       a6 OpenBSD          ee GPT            
0f W95 Extd (LBA)  55 EZ-Drive         a7 NeXTSTEP         ef EFI (FAT-12/16/
10 OPUS             56 Golden Bow       a8 Darwin UFS       f0 Linux/PA-RISC b
11 Hidden FAT12     5c Priam Edisk      a9 NetBSD           f1 SpeedStor      
12 Compaq diagnost  61 SpeedStor        ab Darwin boot      f4 SpeedStor      
14 Hidden FAT16 <3  63 GNU HURD or Sys  af HFS / HFS+       f2 DOS secondary  
16 Hidden FAT16     64 Novell Netware   b7 BSDI fs          f8 EBBR protective
17 Hidden HPFS/NTF  65 Novell Netware   b8 BSDI swap        fb VMware VMFS    
18 AST SmartSleep   70 DiskSecure Mult  bb Boot Wizard hid  fc VMware VMKCORE 
1b Hidden W95 FAT3  75 PC/IX            bc Acronis FAT32 L  fd Linux raid auto
1c Hidden W95 FAT3  80 Old Minix        be Solaris boot     fe LANstep        
1e Hidden W95 FAT1  81 Minix / old Lin  bf Solaris          ff BBT            
24 NEC DOS        

Aliases:
   linux          - 83
   swap           - 82
   extended       - 05
   uefi           - EF
   raid           - FD
   lvm            - 8E
   linuxex        - 85
Hex code or alias (type L to list all): 8e 
Changed type of partition 'Linux' to 'Linux LVM'.
# 我们需要change为代码是 8e（16进制数字）Linux LVM格式
Command (m for help): p
Disk /dev/sdb: 20 GiB, 21474836480 bytes, 41943040 sectors
Disk model: VMware Virtual S
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x907350bf

Device     Boot Start      End  Sectors Size Id Type
/dev/sdb1        2048 41943039 41940992  20G 8e Linux LVM
# 再打印一边看看， 看最后一行 /dev/sdb1 这个确实是Linux LVM 了
Command (m for help): w # 千万别忘了保存变更！
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

接下来创建lvm下的pv vg（不需要创建lv并格式化）

root@slave2:/home/bill# apt install lvm2 #安装lvm2
root@slave2:/home/bill# sudo pvcreate /dev/sdb1 # 创建pv
  Physical volume "/dev/sdb1" successfully created.
root@slave2:/home/bill# sudo pvs
  PV         VG Fmt  Attr PSize   PFree  
  /dev/sdb1     lvm2 ---  <20.00g <20.00g
root@slave2:/home/bill# sudo pvdisplay #显示创建好的pv
  "/dev/sdb1" is a new physical volume of "<20.00 GiB"
  --- NEW Physical volume ---
  PV Name               /dev/sdb1
  VG Name               
  PV Size               <20.00 GiB
  Allocatable           NO
  PE Size               0   
  Total PE              0
  Free PE               0
  Allocated PE          0
  PV UUID               8YdNRX-I9ZR-lXKc-8yvp-OMvN-eZWm-dDecux #PV的uuid
   
root@slave2:/home/bill# sudo vgcreate vg-k8s-test /dev/sdb1 
  Volume group "vg-k8s-test" successfully created
  #为整个磁盘创建为了一个名为 vg-k8s-test 的volume group
  #附加思考：可用将2个物理磁盘创建为一个volume group么 ？ 可用将lv创建在两个不同磁盘的vg上么，能或者不能，各有什么利弊 ？
root@slave2:/home/bill# sudo vgs
  VG          #PV #LV #SN Attr   VSize   VFree  
  vg-k8s-test   1   0   0 wz--n- <20.00g <20.00g
  # vgs命令可看，名为 vg-k8s-test的vg已经存在了，记住整个名字，后面要用到！
root@slave2:/home/bill# sudo vgdisplay
  --- Volume group ---
  VG Name               vg-k8s-test
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  1
  VG Access             read/write
  VG Status             resizable #当然是resizable的了， 这才是lvm的具体优势所在
  MAX LV                0
  Cur LV                0
  Open LV               0
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               <20.00 GiB
  PE Size               4.00 MiB
  Total PE              5119
  Alloc PE / Size       0 / 0   
  Free  PE / Size       5119 / <20.00 GiB
  VG UUID               GWJesr-2Qa8-UMya-4UIF-kkWG-qGGj-Lfe0gt #VG也有自己的uuid
   

也不好少了， 明天将重头戏 也就是k8s如何实现lvm类型的StorageClass讲完。