Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Hi all,
Just thought I'd dig this one up out of the archives as it interests me to
know more on some progress, if it has been made:
> -----Original Message-----
> From: drbd-user-bounces at lists.linbit.com
> [mailto:drbd-user-bounces at lists.linbit.com]On Behalf Of paddy
> Sent: Friday, 1 July 2005 5:05 AM
> To: drbd-user at lists.linbit.com
> Subject: Re: [DRBD-user] 3 simple questions for a nifty setup
>
>
> Hi malte,
>
> I'm no expert, but I am doing similar things so I'll have a stab at
> some answers for you.
>
> On Thu, Jun 30, 2005 at 08:43:48PM +0200, ephigenie at g-house.de wrote:
> > Hello Everyone,
> >
> > I've managed to get drbd-07.11 to work with 2 sarge boxes,
> > but there a few questions open at this point :
> >
> > whenever i try to mount the drbd/0 device on the secondary,
>
> If I understand you correctly, the answer is: you shouldn't do that.
>
> http://wwnew.linux-ha.org/DRBD_2fFAQ#head-ff8f594c0d61552676dd75c5
> c2818546f737f712
>
> nevertheless I got the impression that you could ...
>
> > i get the following ...
> > but the device is not mounted (according to /proc/mounts & mtab etc..)
> > the mountpoint has no influence on that behaviour since when i try
> > an other one, it works ?
>
> sorry don't understand those last two lines (above). Do you mean you can
> mount it okay on the primary ?
>
> > ---snipp----------
> > www-2:/# mount -t ext3 /dev/drbd/0 /ha/
> > mount: block device /dev/drbd/0 is write-protected, mounting read-only
> > mount: /dev/drbd/0 already mounted or /ha/ busy
> > ---snapp----------
>
> aren't mount(1) error message great !
>
> > the second one :
> >
> > i'd like to make some webspace ha - this should work i think
> > but as I'm lazy, i concidered using drbd for a mysql instance
> > but there's my question - are there any problems known with that ?
>
> Don't know if there are know problems but I have such a setup on
> a sarge testbed
> it seems to work (very simple testing), and I'd be happy to share
> my config with you.
>
> My assumptions are:
>
> If drbd does what it says on the packet, then when you start
> mysql after failover
> it shouldn't be any worse than if you restarted after, say, a
> power failure.
>
> I don't how big (or how long) problems might be if mysql do its
> equivalent of
> fsck, so that's a worry. By the looks of it mysql replication is
> not without
> its complications and the cluster mode is out of the question for
> my application.
>
> Having said that, I plan to try out mysql replication and compare
> the results.
Paddy,
Have you made any more progress on your mysql install on top of DRBD yet? I
am interested in doing the same, but if I go the 'proper' mysql cluster way,
I need 3 machines, and I only have 2.
> Since IIUC mysql replication is asyncronous, drbd might even be
> better for some
> values of better.
>
> > for sure i will sort all writeaccess out and direct it to the master
>
> reads too, with drbd you're only going to have one mysql instance
> accessing the
> database at a time. I've yet to figure out what happens at the
> client when the
> connection to the primary get lost, but I expect it'll be okay :)
>
> > but this seems to me more smart than using the mysql - replication
>
> I guess it depends on your load. If you are doing a lot of reads
> then I imagine
> replication could be a big win.
>
> > Is there anyone who has this as a working setup or has
> experiences with that ?
> >
> > the third one :
> > at the moment there are only 2boxes, but a third and a forth a
> prepared ...
> > but i searched the half web for that and had nothing found -
> >
> > so is it possible to have 1 primary and 3 or more secondarys ?
> > What about choosing the next primary - can heartbeat do that job - or is
> > this just for the head-to-head config everywhere mentioned with
> 1 primary and 1
> > secondary ?
>
> my understanding is that drbd will only do 2 machines, although
> I'd be delighted
> to learn otherwise. One of the temptations of mysql replication
> for me is the
> ability to form larger networks of replicas.
Is it possible to have more than 2 members of a resource group? I seem to
remember seeing such an example in this list sometime but I can't find it. I
think the config was something like:
resource r0 {
on machine1 {
device /dev/drbd0;
disk /dev/hdc;
address 192.168.1.1:7788;
meta-disk /dev/hda5 [0];
}
on machine2 {
device /dev/drbd0;
disk /dev/hdc;
address 192.168.1.2:7788;
meta-disk /dev/hda5 [0];
}
on machine3 {
device /dev/drbd0;
disk /dev/hdc;
address 192.168.1.3:7788;
meta-disk /dev/hda5 [0];
}
}
So that, only 1 of machine1/2/3 may be primary at any given time, but the
effect is that of the device /dev/hdc being "mirrored" accross all three
PC's?
Could someone please correct me here if I have this wrong?
Regards,
David.
> There are other similar technologies that do different things. I
> don't any
> experience with them, (so these are _not_ recommendations) but an
> ipcomplete
> list I'm sure:
>
> GNBD/GFS comes to mind as an example of a clustered filesystem
> where you can mount and write at more than one node. I don't
> know whether
> you can run multiple mysql servers against the same backend
> (perhaps with
> a master for the writes ?), somehow I doubt it. IIRC its in
> unstable but
> not sarge (not stable upstream).
>
> ENBD (looks similar to DRBD)
>
> There's also stuff like AFS and coda. Intermezzo looked
> interesting for a while there.
>
> postgresql appears to have similar features to mysql.
>
> of course, its horses for courses.
>
> > thanks for your help
> >
> > malte
>
> hope this does help :)
>
> Regards,
> Paddy
> --
> Perl 6 will give you the big knob. -- Larry Wall
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