[DRBD-user] Persistent Device Names

Jake Smith jsmith at argotec.com
Wed Jan 25 00:04:05 CET 2012

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


----- Original Message -----
> From: "Ted Young" <mail at tedyoung.me>
> To: drbd-user at lists.linbit.com
> Sent: Tuesday, January 24, 2012 5:50:09 PM
> Subject: Re: [DRBD-user] Persistent Device Names
> 
> > Additionally when you mirror disks directly with drbd, your
> > drbd-resources
> are fixed to the size of the disk-pairs. When you mirror lvm volumes,
> they
> can have the size they need to have to fulfill their > task. You can
> have
> drbd-resources of only some MB but also resources of the size of two
> or
> three of your disks toghether.
> 
> Thank you Arnold for your reply.  I think you may have hit the
> impedance
> mismatch on the head!  You are recommending putting DRBD on top of a
> large
> LVM volume.  In fact, I was planning on putting LVM on top of a bunch
> of
> mirrored (DRBD) physical drives.  When one puts DRBD on top of LVM
> one risks
> losing the entire logical volume if a single drive fails.  In such a
> case,
> DRBD would have to re-sync the entire logical volume.  By putting LVM
> on top
> of DRBD, DRBD would only have to re-sync the failed hard drive.
> 
> That being said, I just discovered today that DRBD volumes are a
> relatively
> new feature.  Prior to version 8.4 one would have to create a
> separate DRBD
> resource for every synchronized block device.  Obviously, this would
> be
> really annoying and so using DRBD on top of LVM makes sense.
>  However, I was
> planning on defining each physical hard drive as a DRBD volume within
> one
> resource then using LVM to stripe/aggregate them.  So perhaps the
> reason I
> have found little on the subject is that most people have
> traditionally put
> DRBD on top of LVM instead of the other way around.
> 
> Ted Young

I happen to do DRBD over LVM which I like however there is documentation on doing both... 
LVM -> DRBD -> LVM (however little I may understand of why you would want this)

See the DRBD users guide here for 8.3.x:
http://www.drbd.org/users-guide-legacy/s-nested-lvm.html
or here for 8.4.x:
http://www.drbd.org/users-guide/s-nested-lvm.html

HTH

Jake

> 
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