[DRBD-user] Newbie

Felix Frank ff at mpexnet.de
Thu Feb 10 09:52:20 CET 2011

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


Hi,

On 02/09/2011 06:58 PM, Chris Barnes wrote:
> First, I hope this is ok to post this question in this email list...
> Secondly, I have been reading the Users Guide at
> http://www.drbd.org/users-guide/ - but still have a few "before I start"
> type of questions.
> 
> I am wanting to create a high-availability cluster and I *think* DRBD is
> what I am looking for.   But I'm not quite sure.
> 
> 
> My *thought* was to use DRBD to mirror the /home filesystem between the
> 2 machines - but I have someone working for me that is saying the DRBD
> mirrors "entire systems".   If he is correct, wouldn't that mean that 2
> computers would require the exact same hardware?

it's just not true that DRBD is only for whole-system replication. It's
very common to sync only database directories, DFS shares etc.
Syncing only /home and keeping everything else up-to-date using other
tools like puppet, svn/git etc. makes a lot of sense in many cases!

> Or am I not even thinking of DRBD in the correct terms?  After all, a
> "true high availability cluster" would mean my down time is measured in
> seconds, right?   I would not have that if all I am mirroring is /home...

See above, there are schemes of keeping clustered servers in sync apart
from doing block-level storage replication.

> My systems (if it matters):
> I have one disk array (10TB, Raid5+1) with /home on it's own filesystem
> using 7.2T (according to the df command).  This machine is in production
> and has been in use for a couple of years now.
> 
> I have another system that is completely blank and ready to configure
> any way that makes sense.  It has 2 250gb drives in a hardware Raid0,
> and 8 2tb drives in a hardware Raid5 (currently Raid5+3 - trying to give
> me 8tb of space).

Uhuh - is this a likely combination of RAID levels? I've read something
on this list recently about RAID5 not playing exceptionally well with
DRBD performance-wise.

Other than that, setting up DRBD on this setup shouldn't pose any
problem not covered by the user's guide.

Regards,
Felix



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