How to create RAID on Loop Devices and LVM over top of RAID.
Submitted by Satish Tiwary on Mon, 10/29/2012 - 18:29
Before you go through this article, let me inform you that this is completely experimental.So read it, enjoy it,but use it in real environment at your own risk.I use to do so many experimental things in my Lab and this is just one of them.We have studied and know so much about Partitions,RAID and LVM.This time i am going to write something on the fact which comes out after relating all these things together. As you all know that once we have created LVM on top of RAID, it become so easy to add any other volume to RAID. Now instead of using a real device or real partition here we are going to use loop devices.Then after creating loop devices we will create RAID on loop devices.And after that we will create LVM over top of RAID.
Step by step explanation:-
- First you need to create Loop Devices:
- Then you create new Arrays using these Loop Devices or you can say create RAID Device.
- After that you need to initialize the physical Volume(PV).
- Then you can create Volume Groups(VG).
- After that you create Logical Volumes(LVM).
- Now you can resize the RAID Array.
- You can also resize LVM and RAID and can easily test or verify their sizes after every changes you have made.
- After you complete this experimental Lab, you can delete all these by given process, which i have mentioned in this article at last.
Create three 200mb Files First using dd command.
using dd(Disk Dump command we will create three files each of size 200MB)
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| [root@satish ~]# dd if=/dev/zero of=raid-0 bs=1M count=200200+0 records in200+0 records out209715200 bytes (210 MB) copied, 0.554498 seconds, 378 MB/s |
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| [root@satish ~]# cp raid-0 raid-1[root@satish ~]# cp raid-0 raid-2 |
Create initial array using above three 200mb files by converting them to loop device using losetup command.
losetup command is used to create loop device in linux.
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| [root@satish ~]# losetup /dev/loop0 raid-0[root@satish ~]# losetup /dev/loop1 raid-1[root@satish ~]# losetup /dev/loop2 raid-2 |
Create the new array using these three loop devices.
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| [root@satish ~]# mdadm --create --verbose /dev/md5 --level=5 --raid-devices=3 /dev/loop0 /dev/loop1 /dev/loop2mdadm: layout defaults to left-symmetricmdadm: chunk size defaults to 64Kmdadm: size set to 204736Kmdadm: array /dev/md5 started. |
Using madam command we have created software raid5 using three loop devices named /dev/loop0 /dev/loop1 and /dev/loop2. Now after creating raid we need to confirm whether raid is properly configured or not.So we need to test it and we can do examine that in a very simple way using mdadm command with option --detail as mentioned below.
Now Examine the created raid Devices in Detail.
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| [root@satish ~]# mdadm --detail /dev/md5/dev/md5: Version : 0.90 Creation Time : Wed Jul 31 16:21:01 2013 Raid Level : raid5 Array Size : 409472 (399.94 MiB 419.30 MB) Used Dev Size : 204736 (199.97 MiB 209.65 MB) Raid Devices : 3 Total Devices : 3Preferred Minor : 5 Persistence : Superblock is persistent Update Time : Wed Jul 31 16:22:36 2013 State : clean Active Devices : 3Working Devices : 3 Failed Devices : 0 Spare Devices : 0 Layout : left-symmetric Chunk Size : 64K UUID : 592f15a1:dba02592:c3b644ca:412e7cf4 Events : 0.2 Number Major Minor RaidDevice State 0 7 0 0 active sync /dev/loop0 1 7 1 1 active sync /dev/loop1 2 7 2 2 active sync /dev/loop2 |
Above output clearly show us that the three devices /dev/loop0 /dev/loop1 and /dev/loop2 is active in raid array.
Now initialize the Physical Volumes (PVs) and Create Volume Groups(VGs)
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| [root@satish ~]# pvcreate /dev/md5 Physical volume "/dev/md5" successfully created[root@satish ~]# pvdisplay "/dev/md5" is a new physical volume of "399.88 MB" --- NEW Physical volume --- PV Name /dev/md5 VG Name PV Size 399.88 MB Allocatable NO PE Size (KByte) 0 Total PE 0 Free PE 0 Allocated PE 0 PV UUID ytsDuk-Z1BG-S3tO-3mMy-wAQv-kuTZ-3a5TbM |
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| [root@satish ~]# vgcreate lvm-satish /dev/md5 Volume group "lvm-satish" successfully created |
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| [root@satish ~]# vgdisplay --- Volume group --- VG Name lvm-satish 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 396.00 MB PE Size 4.00 MB Total PE 99 Alloc PE / Size 0 / 0 Free PE / Size 99 / 396.00 MB VG UUID N0d0YK-9sGO-v8jY-9kSL-rFfx-lLCA-VnCqYP |
Create and Examine lvm Volume.
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| [root@satish ~]# lvcreate -l 60 lvm-satish -n lvm0 Logical volume "lvm0" created |
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| [root@satish ~]# lvdisplay --- Logical volume --- LV Name /dev/lvm-satish/lvm0 VG Name lvm-satish LV UUID yMOTeD-1X3S-W5G7-arSn-s6tf-PKD1-y6Bv54 LV Write Access read/write LV Status available # open 0 LV Size 240.00 MB Current LE 60 Segments 1 Allocation inherit Read ahead sectors auto - currently set to 512 Block device 253:0 |
Now Format and mount it on a directory.
here i am going to mount it on slashroot directory.
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| [root@satish ~]# mkfs.ext3 /dev/lvm-satish/lvm0[root@satish ~]# mount /dev/lvm-satish/lvm0 slashroot/[root@satish ~]# df -hFilesystem Size Used Avail Use% Mounted on/dev/sda3 24G 12G 11G 54% /tmpfs 502M 0 502M 0% /dev/shm/dev/mapper/lvm--satish-lvm0 233M 6.1M 215M 3% /root/slashroot |
Now add a File to it.
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| [root@satish ~]# dd if=/dev/zero of=slashroot/ironman3.avi bs=10240 count=1024010240+0 records in10240+0 records out104857600 bytes (105 MB) copied, 0.714737 seconds, 147 MB/s[root@satish ~]# df -hFilesystem Size Used Avail Use% Mounted on/dev/mapper/lvm--satish-lvm0 233M 107M 114M 49% /root/slashroot |
