Re: [DRIVER SUBMISSION] DRBD wants to go mainline

[Tomasz Chmielewski <mangoo@wpkg.org>]

Jan Engelhardt wrote

> On Jul 22 2007 00:43, Lars Ellenberg wrote:

>>Think of it as RAID1 over TCP.
> 
> And what does it do better than raid1-over-NBD? (Which is already N-disk,
> and, logically, seems to support cluster filesystems)

I don't know about DRDB, but NBD doesn't handle network disconnections 
at all (well, almost).

So basically, disconnect a NBD-connected system for a while (switch, 
cabling problem, operator error etc.), and you need lots of effort, 
perhaps restarts, to get the things to a functioning state (devices 
offlined, kicked out etc.).

I wouldn't call such raid-over-NBD setup reliable.


A better question would be: what does it do better than raid1-over-iSCSI?

iSCSI can recover from disconnections very well when configured 
properly; but when a disconnection is in place, most of the system will 
just "hang/freeze" (that is, from the user perspective - the system will 
be waiting for the I/O to complete, until the systems are connected again).


A brief reading of "official DRBD FAQ" didn't give me an answer to that 
problem.


-- 
Tomasz Chmielewski
http://wpkg.org