[linux-lvm] Mirrored LV

[malahal at us.ibm.com]

Jonathan Brassow [jbrassow at redhat.com] wrote:
> Just to answer some questions:
>
> You can use just 2 disks to create a mirror and a disk log:
> prompt> lvcreate --alloc anywhere -m1 -L 500M -n my_lv my_vg
>
> I wish the allocation policy 'normal' (which is the default) would also do 
> this... but instead you must choose a looser allocation policy to get what 
> you want.
>
> The reason that you want the disk-based log is to prevent all the extra 
> work when you machine comes up.

I wish LVM can detect and only re-sync if needed even with corelog!

> The reason that LVM wants a separate disk for the log is so the head on the 
> storage device doesn't need to go ping-ponging around the device.  (The log 
> is touched for almost every write.)  So, its a performance thing... and 
> possibly a not-wear-out-your-hardware thing too.

Nice to know about guaranteed long disk seeks with this approach!

--Malahal.