On 7/11/2011 2:13 PM, Christian Völker wrote:
>
>> Without the lvm snapshots, isn't there a danger of something corrupting
>> the master server's filesystem and having it propagate to the drbd copy
>> instantly?
>>
> You're absolutely right. And this is the reason why I have the LVM
> snapshots. I can go back 5 weeks with the snapshots.  That's enough to
> prevent any serious issues. When the file system gets unreadable I
> usually notice it immediately- and roll back to previous snapshot.
>
> BTW: The same would happen with the often so proposed "take off a disk
> of your RAID1".

The way my 'take a disk off RAID1' works is that there are 3 spare 
disks, with at least one always offsite in the rotation and another one 
wouldn't be brought back if there was any reason to suspect that the 
filesystem was corrupt as copied on the most recent.

> In some way you have to trust the filesystem.

You have to trust that it works when it appears to be working.  You 
don't have to trust it to keep working through your next copy.

> Of course
> rsync'ing it from host A with ext3 to host B with XFS would be a better
> solution security wise. But as you know rsync is not the best solution here.

Even rsync'ing would leave you in a strange state if the source dies in 
mid-copy to your only target.

> I trust my file system at least for 5 weeks ;)

I don't trust anything in the same building or anything that can be 
corrupted by a live copy.  And I don't know enough about lvm to 
understand how you can drbd to the live partition while keeping 
snapshots of old copies.  I wouldn't have expected that to work.  Are 
they really layered correctly so the lvm copy-on-write business works?

-- 
    Les Mikesell
     lesmikesell AT gmail DOT com

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