Should I use raid in a virtual vm set-up

not with minidlna if you serch the forum you can install plex which will transcode.

glad that works for you

As explained in your other thread, building a raid array out of partitions from a single physical drive, will mean a decrease in performance instead of an increase.

Why?

You only have one physical head in your drive.
In a normal non raid situation with one physical drive you can read with the maximum possible speed from that drive for sequential IO (that's what you normally do on a file server).

If you have multiple drives, you can increase your performance by utilizing all disks for reads. So you will split up the file over all disks. Lets assume you have 4 disks. So you will split the file that alternating you putting chunks of it on all drives. Therefore you increase the overall performance.

If you put 4 partitions on a single drive and do the same, the raid software will still do the same, but you will read all the time from the same drive. So the performance naturally will not increase, as the performance is simply limited by the physics of that drive. In reality, cause of the single head in a drive, it will make the situation worse. Instead of constantly reading the next block and the the next block, the head now need to jump between the four partitions. So you not only waiting for the next block to get read, you also waiting for the head to get repositioned before the next block can be read. This will beneath other things kill the caching mechanism of the drive. So if we assume a read speed of about 100MB/s for a drive, it will go down to 10 or 15mb/s ... Not per partition but overall. Virtualization does not make it better, but is also not directly related to this issue.

If you have 4 physical drives even if you do not use them completely for virtual space, you can still setup raid and benefit from the performance gain. But setting up four virtual drives on the same physical drive still does not make any sense.

Hope that gives a little bit better understanding of this complex matter.