[linux-lvm] realtime snapshot or ?

["Omer Faruk Sen" <omer faruk net>]

Hi,

I am looking for a solution that I can use as a realtime snapshot or maybe
it should be called realtime raid or whatever.

What I want is like this:

Say I have a VG1 and VG2. I use VG2 as a backup VG2  and some machines
will mount it as read-only( I mean LV2 on VG2) My main server (which runs
mysql and all write operations will go to LV1) will run mysql and use 
/sql as its --data-dir. /sql uses /dev/VG1/LV1. But every write operations
on LV1 that resides on VG1 should go to VG2 thus to LV2 too.

I have found that nbd ord drbd does similar things. But nbd just exports a
block device (JUST ONE block device) so other machines can mount it. DRBD
is closer to what I want but I can't mount drbd on secondary (backup
machine) even as read-only



To depict what I want
                            rw
|SERVER1| ----> MYSQL DATA ---->    | REMOTE STORAGE | VG1/LV1
                           |
                           |--->    | REMOTE STORAGE | VG2/LV2 --|
                             rw                                  |
                                                                 |
                                                                 |
                                                             ro  |
                                   /backupsql/--- |SERVER2|   <--|






-- 
Omer Faruk Sen
http://www.faruk.net