[linux-lvm] realtime snapshot or ?

[linux-lvm] realtime snapshot or ?

[Omer Faruk Sen]

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

Re: [linux-lvm] realtime snapshot or ?

[Greg Freemyer]

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On 4/30/06, Omer Faruk Sen <omer@faruk.net> wrote:
>
> <snip>
>
> 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


You should check out drbd 0.8 and see if it still has the same restriction.
0.8 is in beta or pre-release.  It is supposed to allow "active/active"
environments.  I believe a clustered FS like GFS is intended to be used with
the new functionality, but it may be that the slave can do a read-only
mount.  If not, you could use GFS as your filesystem and achieve your goal.
The big trouble with that is locking.  I'm pretty sure GFS only does file
locking.  Not very helpful for a DB.

Greg
-- 
Greg Freemyer
The Norcross Group
Forensics for the 21st Century

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