I suspect this isn't a problem that can be solved without having a
proper journal of metadata per directory, so that upon connection, the
whole journal can be replayed.
You could sort of bodge it and use timestamps as the primary version and
the xattr version as secondary, bit that is no less dangerous - it only
takes one machine to be out of sync, and we are again looking at massive
scope for data loss.
You could bodge the bodge further to work around this by ensuring that
the nodes are heartbeating current times to sync between them and
without the sync no data exchange takes place. But that then complicates
things because what do you do when a node connects and is out of sync,
but in the future? Who wins on time sync? Who has the latest
authoritative copy?
I think the most sane way of addressing this is to have a fully logged
directory metadata journal. But then we are back to the journalling for
fast updates issue with a journal shadow volume, which is non-trivial to
implement.
Unless there is some kind of a major mitigating circumstance, it seems
that between this and the race condition that Martin is talking about on
the other thread, GlusterFS in it's current is just too dangerous to use
in most environments that I can think of. And unlike Gareth a few days
ago, I'm not talking about performance issues - I'm talking about scope
for data loss in very valid and very common use cases. :'(
Gordan
Amar S. Tumballi wrote:
I still need time to understand it. But my doubt is that, vi moves the
old file to 'filename~' and then create a new file 'filename'. If this
is the case it will have version 2, as its a new file.
But still, I can think of all disasters it can cause. Let me check with
Avati/Krishna about these.
Regards,
Amar
On Tue, May 6, 2008 at 12:07 PM, <gordan@xxxxxxxxxx
<mailto:gordan@xxxxxxxxxx>> wrote:
Hi,
Maybe I'm missing something important here, but something isn't
making sense to me.
When I create a file on the glusterfs mount, it gets version of "2".
All well and good. If I >> a line to it, it's version ticks up. So
far so good.
If I vi the file, add a line and save it, it's version resets back
to "2"!
What exactly is going on here? I'm sure that there is a perfectly
good explanation here (i.e. that vi removes the file and re-creates
it anew), but I just wanted to make sure this is a sane condition.
Also, would this not mean that following a disconnection, all vi-ed
files would get clobbered when the server reconnects and the file
gets read?! This strikes me as _INCREDIBLY_ dangerous. Too dangerous
for any use, in fact.
Can somebody please tell me that I'm wrong here? Because I really
hope that I am.
