LVM vs Software RAID

Hi everyone,

Quick question: Given that it is now possible to have software-based
RAID arrays which are able to be grown using mdadm on Linux, what
advantage, if any, does LVM actually provide?

And yes, I am aware that the filesystem does not grow with mdadm's
--grow command, but tools like resize2fs seem to be sufficient. :-)

Any thoughts on this?

Thanks,
-Wendell
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Wendell III wrote:
Hi everyone,

Quick question: Given that it is now possible to have software-based
RAID arrays which are able to be grown using mdadm on Linux, what
advantage, if any, does LVM actually provide?

Well, for a start, it lets you grow your underlying storage to arbitrary
sizes without having to grow individual arrays to unreasonable sizes
(e.g., keeping RAID-5 arrays relatively small and striping across
multiple such arrays provides considerably more availability than using
a single large RAID-5 array).

Some LVMs also support inter-site replication between one array (or set
of arrays) and another. Yes, this is something that a driver can
provide (at least for an individual disk or array) as well, but
packaging this up in an LVM can make things easier to work with.

Hmmm - how would multiple arrays (which might support separate file
systems rather than a single file system striped across them) coordinate
shared use of hot-spare disks, rather than require separate spares for
each array?

Perhaps the easiest way to look at it is that an LVM can manage multiple
volumes (and the various ways they can be used together), whereas a RAID
array presents a single volume to the next level up.

- bill