Is Ubuntu LVM a RAID?

Question

I had a 4 disk LAMP system running Ubuntu 10 then upgraded to 12. The drives are managed by LVM since initial setup. Recently, one of the drive failed (the newest and largest of course, 3TB). I sent it to a data recovery service to try to recover the data, now they are telling me that I have a RAID setup and they would need all of my 4 drives to do the recovery, and of course charge me x4 the price.

So I'm a little confused as to why they would need all 4 of my drive to be able to recover my 1 failed disk. As far as I remember I had 2 logical volumes:

• The "System" logical volume contained the Linux OS, and a single physical disk.
• The "Data" logical volume included 3 physical disk, with the "/home" directory entirely on the physical drive that failed. This failed disk contained only my /home directory, although the logical volume contained 2 other disks the /home data is completely contain on that one disk (i.e. not spread to a second physical disk or striped like in a real RAID).

I guess my questions are:

1. Is Ubuntu LVM using some sort of RAID underneath?
2. If not, what would be the reason why the data recovery service would need all of my drives to make the recovery?
3. Can I read the contents of a physical volume that was part of a logical volume (like my failed disk above) independently on a separate machine (like an external HD)?

Answer 1

Is Ubuntu LVM using some sort of RAID underneath?

No, not so far as I know (although it is possible to configure LVM on top of RAID i.e. with one or more RAID arrays as physical volumes - I assume you didn't do that).

If not, what would be the reason why the data recovery service would need all of my drives to make the recovery?

Possibly just that the volume group (VG) could not be activated without all of its constituent physical volumes (PVs) - regardless of whether any of their physical extents were actually allocated to a logical volume (LV).

Can I read the contents of a physical volume that was part of a logical volume (like my failed disk above) independently on a separate machine (like an external HD)?

You would still need to activate the VG I think. I have very limited experience with LVM, however the vgchange manpage mentions a --partial flag that may allow you to activate a VG with one or more of its constituent PVs missing: the option seems to be more fully documented in the lvm (8) manpage man 8 lvm

   -P, --partial
          When set, the tools will do their best to provide access to Vol‐
          ume Groups that are only partially available (one or more Physi‐
          cal  Volumes  belonging to the Volume Group are missing from the
          system).  Where part of a logical volume is missing,  /dev/ioer‐
          ror  will  be  substituted,  and you could use dmsetup(8) to set
          this up to return I/O errors when accessed, or create  it  as  a
          large  block  device of nulls.  Metadata may not be changed with
          this option. To insert a replacement Physical Volume of the same
          or large size use pvcreate -u to set the uuid to match the orig‐
          inal followed by vgcfgrestore(8).

You may also want to look at the vgreduce command, in particular its --removemissing option

   --removemissing
          Removes  all  missing physical volumes from the volume group, if
          there are no logical volumes allocated on  those.  This  resumes
          normal  operation  of  the volume group (new logical volumes may
          again be created, changed and so on).