[Samba] One shared folder to be HA over CIFS to windows clients

[Emiliano Bonassi]

Hi,
i'm Emiliano this is my first mail to samba mailing list.
I have to solve this issue for a company. They need to had a folder, shared
over CIFS for windows/mac clients, that is always available, also if the
server who host it hang up or burn.
I've looked for a lot of solution but i cannot find the right for me.
Actually the company has two server, all running debian lenny as linux
distro.
The first one, a quad core proliant ml350 g5 6tb raid 10, work as primary
server. On it i've installed vmware server that runs a win2003 r2 guest for
central authentication,domain policing ecc. It has another role : the
primary file server, running  a samba server integrated with AD.
The seconde one, a pentium 4 1,2 tb raid 5, work as secondary server. Like
the proliant it has vmware server running a BDC w2k3 r2 for fail-over and
load balancing windows services. Here the file sharing is offered again by a
samba server that shares archive folders.
Now, how can i have the same shared folder on both file servers?
I can adopt microsoft technology : use DFS filesystem and FSR replicas.
Actually, i'm fallen in love with the DFS functionality that permit to
uniform the namespace of file servers resource using only the name of the ad
domain, but i hate the limits of FSR replicas.
Hyp:
- Think that i use DFS and setup that \mydomain\dfs\aaa refer to
\firstserver\aaa and \secondserver\aaa.
- aaa on the firstserver and on the secondserver are the same
- i've setup FSR replicas continuosly between the two shares.

Now, if from one my win client i poll for \mydomain\dfs\aaa , using somekind
of roundrobin\casual algorithm, the DC tell me that \mydomain\dfs\aaa is
\firstserver\aaa or \secondserver\aaa.
Suppose, that DC translate the dfs share with the share on the second file
server, this means that if i open a file gino.txt i'm working on gino.txt on
secondserver.
So now, before the FSR replica, second server got a version of gino.txt
newer than first server.
Now there is a little window of time when if another client ask for the same
dfs share and the same file, it could be possible that DC translate
\mydomain\dfs\aaa with \firstserver\dfs\aaa and this second windows client
works a different version of the file.
Now imagine, that, always before the start of FSR replica, this second
windows client save a modified version of gino.txt .
The FSR algorithm take a decision, "i propagate the newer version of file".
So DFS doesn't work for my situation, i think.

So i ask to you if CTDB samba could work for my problem.
I think no, because i have to have the same configuration (also shares, here
is the problem, i need only one share) between the two fileservers.
I'm trying to test this configuration: using LVM create a LV and mirror with
drbd between two fileserver.
After, put a GFS2 filesystem on them and sharing the filesystem as two
separate shares on the two file servers.
Now i think that DFS could work as a peacemaker to decide which host is up
and translate DFS correctly.
Suppose that i open gino.txt on \1st\aaa , modify it, and save it. If i
setup drbd with the sync mode, instantanously, because the copy it's at the
block level, i have the same file on \2nd\aaa.
But if i open gino.txt on \1st\aaa and gino.txt \2nd\aaa , who tell to the
two usesr that the same file is opened on both fileserver?