[prev in list] [next in list] [prev in thread] [next in thread] 

List:       evms-devel
Subject:    Re: [Evms-devel] Clustering/Private containers with RAID
From:       Ram Pai <linuxram () us ! ibm ! com>
Date:       2003-04-25 18:19:30
[Download RAW message or body]

On Fri, 25 Apr 2003 rschapel@edtech.mcc.edu wrote:

> >
> >
> >>Section 15.1 of the users guide states
> >
> >>Do not assign RAID, snapshot, and BBR features to storage objects on a
> >> cluster container.
> >
> >>I guess I am a little confused by this, while I certainly understand
> >> where software raid could be a problem for shared containers, why
> >> couldn't I use it in a private container? I mean people did this before
> >> there was a "cluster" version of EVMS right? They just manually kept
> >> the two servers from accessing the same container at the same time. Is
> >> there something in using software raid that I am missing?

You are right.  You can have raid/snapshot/bbr features on private
containers, but the only catch is if you do that, 'failover' of the
container is not handled correctly by the software currently.

As long as the private container is not configured for automatic
failover, and failover is done manually with caution(ensuring that the
other node is really dead), I can see it to work just fine.

However we have not tested the failover functionality with these features,
so we cannot say with certainity that it works.  Does anybody see a issue
here?



> Don:
>   Thanks for the info Don, but it sounds like of the troubles that come
> from metadata being kept in memory only happen when the disks are in
> shared containers, and this does make perfect sense to me. I am looking
> at a fail-over solution in which the 2 systems would never share the
> same disk space at the same time , or they would suffer from
> "splitbrain" syndrome. The ares I would use would be kept in private
> containers. I thought this was the whole reason for "shared" and
> "private" containers. This way I can have raid running on  the private
> containers, and only one machine would be able to access the private
> container at the same time. Also there is another rule which states
> 
> "A disk should not span cluster containers"
> 
> Which would stop me from sharing a disk between any two containers whether
> they be shared or private... again this seems to backup where I am going
> here (this rule makes perfect sense to me). Shared containers would need
> to be running something like "openGFS", or similar. I can't even imagine
> the over head that would need to take place to run raid in a shared
> container (egads!)  ...  am I making any sense here?  I am so sorry If I
> am just miss understanding this...

yes. you are making sense throughout! Actually you are think ahead of us.


> 
> It's almost like
> 
> 
> Do not assign RAID, snapshot, and BBR features to storage objects on a
> cluster container.
> 
> should read
> 
> Do not assign RAID, snapshot, and BBR features to storage objects on a
> shared cluster container.

Yes 'Do not assign RAID, snapshot and BBR features to storage objects on
a shared cluster container'.  
And
'Do not configure automatic failover of private containers for private
containers having objects made up of RAID, snapshot and BBR features'

But the latter statement is not validated through tests.


-- 
Ram Pai
linuxram@us.ibm.com
503-5783752
EVMS: http://www.sf.net/projects/evms
----------------------------------



-------------------------------------------------------
This sf.net email is sponsored by:ThinkGeek
Welcome to geek heaven.
http://thinkgeek.com/sf
_______________________________________________
Evms-devel mailing list
Evms-devel@lists.sourceforge.net
To subscribe/unsubscribe, please visit:
https://lists.sourceforge.net/lists/listinfo/evms-devel
[prev in list] [next in list] [prev in thread] [next in thread]