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I am about to set up box to basically be a file server. I plan on having multiple drives in the box, and would like to set them all up so that they appear to be a single drive. So I could essentially have it mounted at say /media and not really care which drive gets used. I am not sure what the correct terminology for doing this is, so my Google fu is useless in this situation.

So how do I set up multiple hard drives to appear as one single drive?

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3 Answers

up vote 10 down vote accepted

You'll probably want to use LVM. You can find some guides here.

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Thanks. As a note it seems the one I want is SettingUpLVM-WithoutACleanInstall as I am not using Raid or encrypting anything. –  jschoen Oct 14 '10 at 1:24
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I decided to write the step by step directions that I did to set this up. An important note is that I did this on a system where I boot from a separate partition that is not part of the LVM. So the LVM is simply for storage and does not have any of the files needed by the OS to boot. Also this is to create the appearance of one large drive, although a similar technique can be used to create the appearance of multiple drives (well partitions really). It is a very selfish brain dump since the other guides do not all that complete to me. So I hope it can help others.

These directions are essentially from the link provided by Murat Gunes with some more information I gathered from here.

I started with a disk that I did not have anything on it that I needed.

  • First you need to create a partition as Linux LVM. You can use fdisk to do this. You can see all the drives Ubuntu sees and how they are listed by running: sudo fdisk -l

The first line in each section should give you enough information to identify your drive. It will look like:

Disk /dev/sda: 500.1 GB, 500107862016 bytes

The part that matters is /dev/sda. Now run: sudo fdisk /dev/sda. You will see:

Command (m for help):

Type p to list the partitions on your drive. You need to delete the partitions that you want to make part of the LVM. So type d to delete. If the drive only has one partition it will remove it (well flag it for removal, it does not happen until we tell it to do it). Otherwise I think (mine only had one) it asks you to enter the number of the one you want to delete.

Now you need to create the new parition. Type n for new. It asks whether extended or primary. Type p for primary. It asks for partition number, type 1. For first cylinder and last cylinder just leave them blank to use the defaults.

Now you need to set it to Linux LVM. Type t. It asks for a hex code, use 8e for the Linux LVM. You shoule see something like:

Changed system type of partition 1 to 8e (Linux LVM)

Finally type w to write out the changes to the disk.

  • Now we need to instal LVM so run sudo apt-get install lvm2 to install it.
  • I am gonna be honest and say I am not sure what this step does but the other directions said to do modprobe dm-mod to Load the LVM Module. I did not get any errors so I figure it worked.
  • We need to edit the /etc/modules file to this module loads on boot. Do sudo nano /etc/modules to open it up to edit. Add dm-mod to the list of items.
  • We also want to edit the lvm configuration to update the filter so it does not take to long to scan (I think that is why anyway). So do sudo nano -w /etc/lvm/lvm.conf and change the line with:

filter = [ "a/.*/" ]

to be:

filter = [ "a|/dev/hd[ab]|", "r/.*/" ]

  • Now we need to set up the first LVM. Do sudo vgscan. You should see something like:

Reading all physical volumes. This may take a while...
No volume groups found

Just in case there are any volume groups already set up run sudo vgchange -a y to make them available. - Now run sudo pvcreate /dev/sda1 to set up the partition. - Now run sudo vgcreate media /dev/sda1 replacing media with the name you want the partition to be labeled as. - Now run sudo lvcreate -l100%FREE -nvolume media replacing volume with the name you want it to be clled. This will use all the free space available in the partition. - Now we need to format the volume so for ext4 you would do sudo mke2fs -t ext4 /dev/media/volume. - Make the directory you want to mount the volume at. I did sudo mkdir /mnt/media. - Mount the volume by doing sudo mount /dev/media/volume /mnt/media. Now this is only for this session. When you reboot it will not be remounted automatically. To do that we need to edit /etc/fstab file. To do this add sudo nano /etc/fstab and add the line:

/dev/media/volume /mnt/media ext4 defaults 0 1

At this point you could start adding files to the disk, so if you need to clear other disks you want to add you could copy them on here.

I separated this out since it is adding a another drive to your volume.

  • So follow the steps in the first bullet again but for this drive.
  • Now if the drive name is /dev/sdb1 then do sudo vgextend media /dev/sdb1 to add it to the volume.
  • Now we need to unmount the volume. To do this do sudo umount /dev/media/volume.
  • Now you can see the stats on your volume now by running sudo vgdisplay. The important part is Free PE / Size. You need to know how much space you can add to the volume for the next step.
  • So if you had 150 Gb of space you would do sudo lvextend -L+150G /dev/media/volume.
  • Now run sudo e2fsck -f /dev/media/volume to check the filesystem.
  • Now run sudo resize2fs /dev/media/volume to resize everything.
  • You can run the stats again and verify that Free PE / Size has dropped to what you expect.
  • Remount the volume by doing sudo mount /dev/media/volume /mnt/media
  • Rinse and repeat for any other drives.
    Also something that I found helpful was I had files I needed to copy off of disks to the LVM I created before I added that disk. So I used cp -r -v so that it would recursively copy files and use the verbose output so I know what it was doing. An example of the full command would be:

cp -r -v /mnt/temp/Movies /mnt/shared/media

Where /mnt/temp/Movies is the folder you want to copy from.

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Quick question...once the LVM is made, say with two drives do you just complete the same steps add any other drives later on? –  user54925 Apr 14 '12 at 13:54
@Craig That is correct. –  jschoen Apr 16 '12 at 12:17
When issuing pvcreate /dev/sda1 I was getting the following: Device /dev/sda1 not found (or ignored by filtering). ...as per launchpad bug #136830 ...the filter in lvm.con [ "a|/dev/hd[ab]|", "r/.*/" ] ...actually needed to read: [ "a|/dev/[hs[d[ab]|", "r/.*/" ] Otherwise, thanks a lot - good how-to. C. –  user178697 Jul 26 '13 at 18:04
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Personally I would make sure all drives are (about) the same size, and create a RAID 5 "array" from them instead. The disadvantage of RAID 5 is that you lose the size of one disk in total available diskspace. The advantage of RAID 5 is that if one of your disks dies, you don't lose a thing, and you can simply replace the broken HDD.

If you don't care enough about losing data to spend an extra disk on it, or if you were planning to use a bunch of disks of different sizes you already have, it's probably best to use LVM, as Murat says.

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Thanks for the tip. I actually have a few drives laying around that are all different sizes. So this was basically to just find a use for them. While it would suck if I lost some stuff on them, it is nothing important that I couldn't replace with minimal effort, and the stuff that is important to me is backed up already. But +1 for a tip that may be useful to others. –  jschoen Oct 14 '10 at 1:50
mdadm ftw. It's a software RAID controller that supports nice things like levels 5 and 6. "RAID isn't a backup" but it's certainly a lot easier to recover from when a drive dies, you just throw in another one, wait a long period of time while it resyncs and you're up and away. You can resync with live disks but it's exponentially slower. –  Oli Oct 17 '10 at 17:37
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