[Gluster-devel] Gluster Recovery

[Sebastien LELIEVRE]

Anand Avati a écrit :
> 
>> Let's continue with this scenario: what would happen if one of the clients
>> changed hello.c again, and the failed server came up again after some
>> extended repair period?
>>
>> What exactly would be the criteria for file resync? (Imagine one of the
>> copies got corrupted during fsck, while still carrying identical metadata
>> information)
> 
> a server which had 'gone down' is not put in operation until it
> undergoes an FSCK. the one with the latest mtime is the 'freshest'
> copy. 
> 
> 
> avati
> 

Let's take the same configuration (we assume that self heal translator
is on) with this scenario :

Client1 is writing a huge file on the afr volume (like 200Mb file size)

Let's say that during this writing (that will take some time), Server 2
goes down, and then comes back a little after but *before* the wrting is
completed.

As you said, Server2 will not be "up" until a successful fsck is performed.

As I understood it, fsck could be performed only if no clients access
the afr volume in some ways.

So then, what would happen if Client2 is a service that continuously
write something on the afr volume ? (like database insertions, or mail
generation, or simply a real-time log of something..)

Will Server2 never come up ?

Here is another scenario :

Client1 and Client2 are accessing the AFR for different manners. (for
instance, one is a mail service that writes everything that come through
and the other is a database)
Is there anything like a load-balancing process or are both clients
writes on server1 which instantly replicates ?

What happen if the link between the 2 servers is severed ?

Let's say that Client1 can still access the volume through Server1,
Client2 only through Server2, AND Server1 can't comunicate with Server2
(what a worse-case-scenario !)

And last but not least : let's now say that Client1 and Client2 run the
same service (= access the same data). What would happen ? (Isn't that
what you've called "split brain" ?)

I have another scenario, but I think it's enough for now, don't you ?

So Sorry,

Enkahel

Sebastien LELIEVRE
slelievre at tbs-internet.com           Services to ISP
TBS-internet                   http://www.TBS-internet.com/