Configuring LVM on top of RAID : An alternative way to partitioning RAID Devices.

Satish Tiwary's picture

Is partitioning raid device is same as partition ext2,ext3 and ext4 file systems?

Answer is NO!
partitioning of raid device is not as same as partitioning of ext2, ext3 and ext4 file systems.

Raid device partitioning is different than simple file system partitioning method.


Why do we need to partition RAID Device?

Partitioning RAID devices is not the same as partitiong simple disk. So what to do when you need to partition a raid device or to resize it.

Creating LVM over top of RAID is one of alternative way to partition RAID Devices.

As we all know tha logical volumes can be created by using single physical volumes or by using multiple physical volumes. So if we have created a logical volume of 100GB using one physical volume and another 100Gb logical volume using multiple physical volume, then in this case which logical volume have higher performance?

or which logical volume is more flexible?

or which logical volume is more stable (i.e minimum chance of data loss)?

or is there will be any change in performance?

You can get the answer of above metioned questions yourself after going through this experimental Lab.

You can test this scenarion on your own machine and Let put your views, your answer here for the rest of world.

This is an experimental Lab which i am going to explain here, but it reveals some conept of raid and lvm, that's why i have decided to publish it. Everyone is free to comment or appreciate on it through comment section, but since this is completely my article so i keep the whole right to ignore the comments if i don't like it and appreciate those who practice this Lab at their lab and share their views,results and ideas here with rest of world.

 

To create  LVM on top of Software RAID5 we need to go through few simple steps which i have mentioned below.

  • Partitioning
  • Changing partition type to raid
  • Configure Software RAID5.
  • Create MD Device /dev/mdX.
  • Choose or Select device Type.
  • Choose number of devices to be used in Raid5.
  • Choose spare device to used in RAID5.
  • Change or configure the Layout of RAID5 Array.
  • Configure mount point.
  • Physical Volume Creation using RAID.
  • Volume Group creation using RAID.
  • Logical Volume creation.
  • format Logical Volume and Configure mount point.
  • Make entry in /etc/fstab file for permanent entry.
  • Test disk failure condition and it's effect on created raid and logical volume.

Step1:- We will create 4 partitions /dev/sda6 /dev/sda7 /dev/sda8 and /dev/sda9  here each of  size 100mb.

 

[root@satish ~]# fdisk /dev/sda

The number of cylinders for this disk is set to 19457.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)

Command (m for help): n
First cylinder (18869-19457, default 18869):
Using default value 18869
Last cylinder or +size or +sizeM or +sizeK (18869-19457, default 19457): +100M

Command (m for help): n
First cylinder (18882-19457, default 18882):
Using default value 18882
Last cylinder or +size or +sizeM or +sizeK (18882-19457, default 19457): +100M

Command (m for help): n
First cylinder (18895-19457, default 18895):
Using default value 18895
Last cylinder or +size or +sizeM or +sizeK (18895-19457, default 19457): +100M

Command (m for help): n
First cylinder (18908-19457, default 18908):
Using default value 18908
Last cylinder or +size or +sizeM or +sizeK (18908-19457, default 19457): +100M

Command (m for help): p

Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      102400    7  HPFS/NTFS
Partition 1 does not end on cylinder boundary.
/dev/sda2              13        3825    30617600    7  HPFS/NTFS
/dev/sda3            3825       11474    61440000    7  HPFS/NTFS
/dev/sda4           11475       19457    64123447+   5  Extended
/dev/sda5           11475       18868    59392273+  83  Linux
/dev/sda6           18869       18881      104391   83  Linux
/dev/sda7           18882       18894      104391   83  Linux
/dev/sda8           18895       18907      104391   83  Linux
/dev/sda9           18908       18920      104391   83  Linux

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.
Syncing disks.


[root@satish ~]#partprobe


Step2:- Change the partition type.

[root@satish ~]# fdisk /dev/sda

The number of cylinders for this disk is set to 19457.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)

Command (m for help): t
Partition number (1-9): 9
Hex code (type L to list codes): fd
Changed system type of partition 9 to fd (Linux raid autodetect)

Command (m for help): t
Partition number (1-9): 8
Hex code (type L to list codes): fd
Changed system type of partition 8 to fd (Linux raid autodetect)

Command (m for help): t
Partition number (1-9): 7
Hex code (type L to list codes): fd
Changed system type of partition 7 to fd (Linux raid autodetect)

Command (m for help): t
Partition number (1-9): 6
Hex code (type L to list codes): fd
Changed system type of partition 6 to fd (Linux raid autodetect)

Command (m for help): p

Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      102400    7  HPFS/NTFS
Partition 1 does not end on cylinder boundary.
/dev/sda2              13        3825    30617600    7  HPFS/NTFS
/dev/sda3            3825       11474    61440000    7  HPFS/NTFS
/dev/sda4           11475       19457    64123447+   5  Extended
/dev/sda5           11475       18868    59392273+  83  Linux
/dev/sda6           18869       18881      104391   fd  Linux raid autodetect
/dev/sda7           18882       18894      104391   fd  Linux raid autodetect
/dev/sda8           18895       18907      104391   fd  Linux raid autodetect
/dev/sda9           18908       18920      104391   fd  Linux raid autodetect

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.
Syncing disks.
[root@satish ~]#partprobe

 

Step3:- Create Raid device initial array using three 100mb partitions /dev/sda6 /dev/sda7 and /dev/sda8.

 

And at the same time we have created the spare device /dev/sda9.

[root@satish ~]# mdadm --create --verbose /dev/md5 --chunk=128 --level=5 --layout=right-asymmetric --raid-devices=3 /dev/sda6 /dev/sda7 /dev/sda8 --spare-devices=1 /dev/sda9


mdadm: /dev/sda6 appears to contain an ext2fs file system
    size=208640K  mtime=Mon May 27 08:20:52 2013
mdadm: /dev/sda6 appears to be part of a raid array:
    level=raid0 devices=2 ctime=Mon May 27 08:11:06 2013
mdadm: /dev/sda7 appears to be part of a raid array:
    level=raid0 devices=2 ctime=Mon May 27 08:11:06 2013
mdadm: /dev/sda8 appears to contain an ext2fs file system
    size=104320K  mtime=Tue May 28 07:49:32 2013
mdadm: /dev/sda8 appears to be part of a raid array:
    level=raid1 devices=2 ctime=Tue May 28 07:48:03 2013
mdadm: /dev/sda9 appears to contain an ext2fs file system
    size=104320K  mtime=Tue May 28 07:49:32 2013
mdadm: /dev/sda9 appears to be part of a raid array:
    level=raid1 devices=2 ctime=Tue May 28 07:48:03 2013
mdadm: size set to 104320K
Continue creating array? y
mdadm: array /dev/md5 started.

EXPLANATION OF THE ABOVE COMMAND:

--create: This option is used to create new raid device.

--verbose:This option helps us to live view the operation information.

--level=5: This options define the RAID level. so here it's RAID5.

--raid-devices=3: This tells us about the number of devices or disks going to be used in raid. here number of disks are 3.

/dev/sda6 /dev/sda7 /dev/sda8: these are the disks which is going to be used in raid here.

--spare-devices: This option is used to add the spare disks while creating the raid array so that in case of disk failure it automatically get sync.

--layout:this option tells about the layout or symmetric of the created array.

 

Step4:- Format the raid devices with journal file system.

[root@satish ~]# mkfs.ext3 /dev/md5
mke2fs 1.39 (29-May-2006)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
52208 inodes, 208640 blocks
10432 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67371008
26 block groups
8192 blocks per group, 8192 fragments per group
2008 inodes per group
Superblock backups stored on blocks:
        8193, 24577, 40961, 57345, 73729, 204801

Writing inode tables: done                            
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 37 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

Step5:- Reviewing the RAID Configuration

How to view or display the basic information of all presently active raid devices.

[root@satish ~]# cat /proc/mdstat
Personalities : [raid0] [raid6] [raid5] [raid4]
md5 : active raid5 sda8[2] sda9[3](S) sda7[1] sda6[0]
      208640 blocks level 5, 128k chunk, algorithm 1 [3/3] [UUU]
      
unused devices: <none>

View the detail information of a raid device.

[root@satish ~]# mdadm --detail /dev/md5
/dev/md5:
        Version : 0.90
  Creation Time : Mon Jun  3 01:22:14 2013
     Raid Level : raid5
     Array Size : 208640 (203.78 MiB 213.65 MB)
  Used Dev Size : 104320 (101.89 MiB 106.82 MB)
   Raid Devices : 3
  Total Devices : 4
Preferred Minor : 5
    Persistence : Superblock is persistent

    Update Time : Mon Jun  3 01:30:52 2013
          State : clean
 Active Devices : 3
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 1

         Layout : right-asymmetric
     Chunk Size : 128K

           UUID : 74a1ed87:c7567887:280dbe38:ef27c774
         Events : 0.2

    Number   Major   Minor   RaidDevice State
       0       8        6        0      active sync   /dev/sda6
       1       8        7        1      active sync   /dev/sda7
       2       8        8        2      active sync   /dev/sda8

       3       8        9        -      spare   /dev/sda9

 

How to determine a given or mentioned device is a component device or a raid device.

[root@satish ~]# mdadm --query /dev/sda9
/dev/sda9: is not an md array
/dev/sda9: device 3 in 3 device active raid5 /dev/md5.  Use mdadm --examine for more detail.

[root@satish ~]# mdadm --query /dev/sda6
/dev/sda6: is not an md array
/dev/sda6: device 0 in 3 device active raid5 /dev/md5.  Use mdadm --examine for more detail.

 

How to determine a given or mentioned device is a component device or a raid device.

[root@satish ~]# mdadm --query /dev/md5
/dev/md5: 203.75MiB raid5 3 devices, 1 spare. Use mdadm --detail for more detail.
/dev/md5: No md super block found, not an md component.

 

How to examine the devices used in raid in more detail.

[root@satish ~]# mdadm --examine /dev/sda9
/dev/sda9:
          Magic : a92b4efc
        Version : 0.90.00
           UUID : 74a1ed87:c7567887:280dbe38:ef27c774
  Creation Time : Mon Jun  3 01:22:14 2013
     Raid Level : raid5
  Used Dev Size : 104320 (101.89 MiB 106.82 MB)
     Array Size : 208640 (203.78 MiB 213.65 MB)
   Raid Devices : 3
  Total Devices : 4
Preferred Minor : 5

    Update Time : Mon Jun  3 01:22:28 2013
          State : clean
 Active Devices : 3
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 1
       Checksum : 9fb5233f - correct
         Events : 2

         Layout : right-asymmetric
     Chunk Size : 128K

      Number   Major   Minor   RaidDevice State
this     3       8        9        3      spare   /dev/sda9

   0     0       8        6        0      active sync   /dev/sda6
   1     1       8        7        1      active sync   /dev/sda7
   2     2       8        8        2      active sync   /dev/sda8
   3     3       8        9        3      spare   /dev/sda9

 

How to list array lines.

[root@satish ~]# mdadm --detail --scan
ARRAY /dev/md5 level=raid5 num-devices=3 metadata=0.90 spares=1 UUID=74a1ed87:c7567887:280dbe38:ef27c774

 

How to view or list array line for a particular device.

[root@satish ~]# mdadm --detail --brief /dev/md5
ARRAY /dev/md5 level=raid5 num-devices=3 metadata=0.90 spares=1 UUID=74a1ed87:c7567887:280dbe38:ef27c774

 

Step6:Create Physical Volume using RAID5 array.

[root@satish ~]# pvcreate /dev/md5
  Physical volume "/dev/md5" successfully created

 

Check Physical volume attributes using pvs.

[root@satish ~]# pvs
  PV         VG   Fmt  Attr PSize   PFree  
  /dev/md5        lvm2 --   203.75M 203.75M

Check Physical Volume information in detail using pvdisplay command.

[root@satish ~]# pvdisplay
  "/dev/md5" is a new physical volume of "203.75 MB"
  --- NEW Physical volume ---
  PV Name               /dev/md5
  VG Name               
  PV Size               203.75 MB
  Allocatable           NO
  PE Size (KByte)       0
  Total PE              0
  Free PE               0
  Allocated PE          0
  PV UUID               e5YCQh-0IFd-MYv2-2WzC-KHEx-pys3-z8w2Ud

 

Step7:- Create volume group named raid5 using vgcreate command.

[root@satish ~]# vgcreate raid5 /dev/md5
  Volume group "raid5" successfully created
You have new mail in /var/spool/mail/root

See Volume group attributes using vgs command.

[root@satish ~]# vgs
  VG    #PV #LV #SN Attr   VSize   VFree  
  raid5   1   0   0 wz--n- 200.00M 200.00M

See volume Group information in detail using vgdisplay.

[root@satish ~]# vgdisplay
  --- Volume group ---
  VG Name               raid5
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  1
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                0
  Open LV               0
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               200.00 MB
  PE Size               4.00 MB
  Total PE              50
  Alloc PE / Size       0 / 0   
  Free  PE / Size       50 / 200.00 MB
  VG UUID               om3xvw-CGQX-mMwx-K03R-jf2p-zaqM-xjswMZ


Step8:- Logical Volume Creation using lvcreate.

[root@satish ~]# lvcreate -L 150M raid5 -n lvm0
  Rounding up size to full physical extent 152.00 MB
  Logical volume "lvm0" created

 

View the attributes of Logical Volume.

 

[root@satish ~]# lvs
  LV   VG    Attr   LSize   Origin Snap%  Move Log Copy%  Convert
  lvm0 raid5 -wi-a- 152.00M    

View Logical Volume information in detail.                              

[root@satish ~]# lvdisplay
  --- Logical volume ---
  LV Name                /dev/raid5/lvm0
  VG Name                raid5
  LV UUID                UCrVf9-3cJx-0TlU-aSl0-Glqg-jOec-UHtVgg
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                152.00 MB
  Current LE             38
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     1024
  Block device           253:0

 

Step9:- Format lvm partition.

[root@satish ~]# mkfs.ext3 /dev/raid5/lvm0
mke2fs 1.39 (29-May-2006)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
38912 inodes, 155648 blocks
7782 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67371008
19 block groups
8192 blocks per group, 8192 fragments per group
2048 inodes per group
Superblock backups stored on blocks:
        8193, 24577, 40961, 57345, 73729

Writing inode tables: done                            
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 22 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

 

Step10:- Configure mount point.

[root@satish ~]# mkdir /raid5
[root@satish ~]# mount /dev/raid5/lvm0 /raid5
[root@satish ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda5              55G   22G   31G  41% /
tmpfs                 502M     0  502M   0% /dev/shm
/dev/mapper/raid5-lvm0
                      148M  5.6M  135M   4% /raid5


Now you can scan all devices

[root@satish ~]# lvmdiskscan
  /dev/ramdisk    [       16.00 MB]
  /dev/raid5/lvm0 [      152.00 MB]
  /dev/ram        [       16.00 MB]
  /dev/sda1       [      100.00 MB]
  /dev/ram2       [       16.00 MB]
  /dev/sda2       [       29.20 GB]
  /dev/ram3       [       16.00 MB]
  /dev/sda3       [       58.59 GB]
  /dev/ram4       [       16.00 MB]
  /dev/ram5       [       16.00 MB]
  /dev/root       [       56.64 GB]
  /dev/md5        [      203.75 MB] LVM physical volume
  /dev/ram6       [       16.00 MB]
  /dev/ram7       [       16.00 MB]
  /dev/ram8       [       16.00 MB]
  /dev/ram9       [       16.00 MB]
  /dev/ram10      [       16.00 MB]
  /dev/ram11      [       16.00 MB]
  /dev/ram12      [       16.00 MB]
  /dev/ram13      [       16.00 MB]
  /dev/ram14      [       16.00 MB]
  /dev/ram15      [       16.00 MB]
  3 disks
  18 partitions
  0 LVM physical volume whole disks
  1 LVM physical volume

Note: Configuration File for lvm is:

[root@satish ~]# vim /etc/lvm/lvm.conf

If you want to know about the physical volume in detail along with the drive participated with physical volume you can get all through this file.This file will you help you understand physical volume creation in detail and helps you in troubleshooting.

[root@satish ~]# vim /etc/lvm/archive/vg00_00000.vg

 1 # Generated by LVM2 version 2.02.46-RHEL5 (2009-06-18): Sat Apr 27 12:45:46 2013
  2
  3 contents = "Text Format Volume Group"
  4 version = 1
  5
  6 description = "Created *before* executing 'vgcreate vg00 /dev/sda6 /dev/sda7 /dev/sda8'"
  7
  8 creation_host = "localhost.localdomain" # Linux localhost.localdomain 2.6.18-164.el5 #1 SMP Tue Aug 18 15:51:54 EDT 2009     i686
  9 creation_time = 1367081146      # Sat Apr 27 12:45:46 2013
 10
 11 vg00 {
 12         id = "H3FYcT-1u28-i8ln-ehNm-DbFM-nelQ-3UFSnw"
 13         seqno = 0
 14         status = ["RESIZEABLE", "READ", "WRITE"]
 15         flags = []
 16         extent_size = 8192              # 4 Megabytes
 17         max_lv = 0
 18         max_pv = 0
 19
 20         physical_volumes {
 21
 22                 pv0 {
 23                         id = "cfz6P0-VVhD-fWUs-sbRj-0pgM-F0JM-76iVOg"
 24                         device = "/dev/sda6"    # Hint only
 25
 26                         status = ["ALLOCATABLE"]
 27                         flags = []
 28                         dev_size = 208782       # 101.944 Megabytes
 29                         pe_start = 384
 30                         pe_count = 25   # 100 Megabytes
 31                 }
 32
 33                 pv1 {
 34                         id = "FiouR5-VRUL-uoFp-6DCS-fJG0-cbUx-7S0gzk"
 35                         device = "/dev/sda7"    # Hint only
 36
 37                         status = ["ALLOCATABLE"]
 38                         flags = []
 39                         dev_size = 208782       # 101.944 Megabytes
 40                         pe_start = 384
 41                         pe_count = 25   # 100 Megabytes
 42                 }
 43
 44                 pv2 {
 45                         id = "oxIjRC-rQGQ-4kHH-K8xR-lJmn-lYOb-x3nYFR"
 46                         device = "/dev/sda8"    # Hint only
 47
 48                         status = ["ALLOCATABLE"]
 49                         flags = []
 50                         dev_size = 208782       # 101.944 Megabytes
 51                         pe_start = 384
 52                         pe_count = 25   # 100 Megabytes
 53                 }
 54         }
 55
 56 }

 


Step11:- for permanent mounting make entry in /etc/fstab file.

add the below line in /etc/fstab file

/dev/raid5/lvm0   /raid5      ext3            defaults     0      0

 

   EXPERIMENTAL FACTS:

What if one of partition involved in raid configuration go to faulty spare?

Let's mannualy i am goint to fail partition /dev/sda8 for testing purpose to see the result of it's effect on raid and lvm.

[root@satish ~]# mdadm /dev/md5 --fail /dev/sda8
mdadm: set /dev/sda8 faulty in /dev/md5

Now you can see the raid array information which clearly show you that spare device we have mentioned at the time of raid device creation automatticaly replace the faulty device.So you can see spare rebuilding option.

[root@satish ~]# mdadm --detail /dev/md5
/dev/md5:
        Version : 0.90
  Creation Time : Mon Jun  3 01:22:14 2013
     Raid Level : raid5
     Array Size : 208640 (203.78 MiB 213.65 MB)
  Used Dev Size : 104320 (101.89 MiB 106.82 MB)
   Raid Devices : 3
  Total Devices : 4
Preferred Minor : 5
    Persistence : Superblock is persistent

    Update Time : Mon Jun  3 02:29:18 2013
          State : clean, degraded, recovering
 Active Devices : 2
Working Devices : 3
 Failed Devices : 1
  Spare Devices : 1

         Layout : right-asymmetric
     Chunk Size : 128K

 Rebuild Status : 21% complete

           UUID : 74a1ed87:c7567887:280dbe38:ef27c774
         Events : 0.4

    Number   Major   Minor   RaidDevice State
       0       8        6        0      active sync   /dev/sda6
       1       8        7        1      active sync   /dev/sda7
       4       8        9        2      spare rebuilding   /dev/sda9

       3       8        8        -      faulty spare   /dev/sda8

Data rebuilding take some time. That's why when you see the result after some time you find that partition now get completely synchronized with raid array.

[root@satish ~]# mdadm --detail /dev/md5
/dev/md5:
        Version : 0.90
  Creation Time : Mon Jun  3 01:22:14 2013
     Raid Level : raid5
     Array Size : 208640 (203.78 MiB 213.65 MB)
  Used Dev Size : 104320 (101.89 MiB 106.82 MB)
   Raid Devices : 3
  Total Devices : 4
Preferred Minor : 5
    Persistence : Superblock is persistent

    Update Time : Mon Jun  3 02:29:31 2013
          State : clean
 Active Devices : 3
Working Devices : 3
 Failed Devices : 1
  Spare Devices : 0

         Layout : right-asymmetric
     Chunk Size : 128K

           UUID : 74a1ed87:c7567887:280dbe38:ef27c774
         Events : 0.6

    Number   Major   Minor   RaidDevice State
       0       8        6        0      active sync   /dev/sda6
       1       8        7        1      active sync   /dev/sda7
       2       8        9        2      active sync   /dev/sda9

       3       8        8        -      faulty spare   /dev/sda8

 

Now you can see the list of active devices and faulty devices here.

[root@satish ~]# cat /proc/mdstat
Personalities : [raid0] [raid6] [raid5] [raid4]
md5 : active raid5 sda8[3](F) sda9[2] sda7[1] sda6[0]
      208640 blocks level 5, 128k chunk, algorithm 1 [3/3] [UUU]
      
unused devices: <none>


 

you find no change in logical Volume.

 

[root@satish ~]# lvdisplay
  --- Logical volume ---
  LV Name                /dev/raid5/lvm0
  VG Name                raid5
  LV UUID                UCrVf9-3cJx-0TlU-aSl0-Glqg-jOec-UHtVgg
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                152.00 MB
  Current LE             38
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     1024
  Block device           253:0

[root@satish ~]# pvck /dev/md5
  Found label on /dev/md5, sector 1, type=LVM2 001
  Found text metadata area: offset=4096, size=258048


There is no loss of data.

[root@satish raid5]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda5              55G   22G   31G  41% /
tmpfs                 502M     0  502M   0% /dev/shm
/dev/mapper/raid5-lvm0
                      148M   56M   84M  40% /raid5

 

Linux Software RAID and DATA Recovery:

we have configure lvm on top of raid very easily, but in the case of crash or data loss we need to recover our data. so data become important.So here we get introduce with the configuration file when lvm is created over raid because this file helps us to understand about the lvm creation and algorithm in detail.

[root@satish ~]# vim /etc/lvm/backup/raid5

  1 # Generated by LVM2 version 2.02.46-RHEL5 (2009-06-18): Mon Jun  3 02:08:05 2013
  2
  3 contents = "Text Format Volume Group"
  4 version = 1
  5
  6 description = "Created *after* executing 'lvcreate -L 150M raid5 -n lvm0'"
  7
  8 creation_host = "satish.com"    # Linux satish.com 2.6.18-164.el5 #1 SMP Tue Aug 18 15:51:54 EDT 2009 i686
  9 creation_time = 1370239685      # Mon Jun  3 02:08:05 2013
 10
 11 raid5 {
 12         id = "om3xvw-CGQX-mMwx-K03R-jf2p-zaqM-xjswMZ"
 13         seqno = 2
 14         status = ["RESIZEABLE", "READ", "WRITE"]
 15         flags = []
 16         extent_size = 8192              # 4 Megabytes
 17         max_lv = 0
 18         max_pv = 0
 19
 20         physical_volumes {
 21
 22                 pv0 {
 23                         id = "e5YCQh-0IFd-MYv2-2WzC-KHEx-pys3-z8w2Ud"
 24                         device = "/dev/md5"     # Hint only
 25
 26                         status = ["ALLOCATABLE"]
 27                         flags = []
 28                         dev_size = 417280       # 203.75 Megabytes
 29                         pe_start = 512
 30                         pe_count = 50   # 200 Megabytes
 31                 }
 32         }
 33
 34         logical_volumes {
 35
 36                 lvm0 {
 37                         id = "UCrVf9-3cJx-0TlU-aSl0-Glqg-jOec-UHtVgg"
 38                         status = ["READ", "WRITE", "VISIBLE"]

 

How to DELETE the above scenario Now.

 Deletion will be done in few simple steps:

  • Step1:remove the line from /etc/fstab file.
  • Step2:unmount the lvm.
  • Step3:remove the lvm using lvremove command.
  • Step4:remove the volume group using vgremove command.
  • step5:remove the physical volume using pvremove command.
  • step6:Now fail the partition used in raid.
  • Step7:Then stop the array.
  • Step8:Then remove the array.
  • Step9:Now delete the partition using fdisk utility.

 

The above process can also be done by creating a loop device instead of using any partition or  any disk. To know how to do the same Lab without creating any new partition or without using any new disk read the article give below:

How to create RAID on Loop Devices and LVM over top of RAID.

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Comments

Very clearly described about RAID and LVM..awesome job man!!

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