[Linux] Losetup and raw devices

[linux@flux.org]

Quoting Frost Jack <sannmateo@yahoo.com>:

> Hello All,
>
> I have a test box (Centos) which i am trying to set up
> Oracle ASM using raw devices. I only have one disk so
> I have created virtual disks using dd if=3D/dev/zero
> of=3D/asmdisks/_file_disk1, etc, etc.. Once the file is
> created I am using losetup to associate it to a
> loopback device. Then lastly I am binding the files
> raw devices using 'raw'. Here is my issue, after I
> reboot all is lost. The raw directory is gone. So then
> I tried using ASMLib which entails the steps above
> except the 'raw' step. But every time I reboot
> /dev/oracleasm/disks shows no contents.
>
> Any assistance would be great.
>
> Matt

Matt:
    As Kevin informed, you'll need to perform the steps on bootup to =20
associate the file to the loopback. However, keep in mind that =20
loopback performance is quite a bit slower than carving out an LVM =20
volume.  I ran a few tests to verify this by creating a 50M LVM volume =20
and a 50M loopback volume. For a 25M write, the LV averages were =20
bouncing between 60-100M/s, where the loopback is running 30-50M/s. =20
I'll run some proper tests later, but it does appear that there's =20
siginificantly more overhead on the loopback.

KL