Red Hat

Hi All,

Hope someone can help me with this.

I have noticed that on some of the servers i am currently administering there is a difference in the setup of some of the LVM disks.

Some of the disks have been created by SN disk allocated, disk partitioned using type 8e over the entire disk, then pv/vg/lv create being completed on the 8e disk.

Others have been setup without the fdisk step so pc/vg/lv creation has been done direct onto raw SAN disk.

There is supposed to be a performance increase by using raw disk as the OS.

So my question is, do you still get performance a increase when using LVM on raw disk the same as you would by using raw disk directly?

And should LVM be created onto raw disk or onto a partitioned device if there is no performance benefit? Is there any best practice around this, there are plenty of guides on how to set this up but nothing to say which way is preferable.

Thanks in advance.
Tom

From what I've seen it has more to do with the app and sometimes the OS in question. Oracle on Solaris benefits decidedly from raw when there is a heavy I/O load on the LVM's for a large db.

It can introduce issues for things like restores. There is also the O_DIRECT flag in Linux, which bypasses the filesystem and does what raw does elsewhere. Assuming your apps can make use of it.

Here is a discussion:
Using Raw Device Partitions

Thanks Jim,

Is there an advantage of having the disk partitioned instead of having a raw disk or would there be any reason partition your disk if you are using the entire disk to add to LVM?

If you get better performance with raw disk and no benefit of partitioning the disk it seems like more work for a worse solution to bother partitioning them (i know not much work but there are quite a few disks per server).