[DRBD-user] Persistent Device Names

Arnold Krille arnold at arnoldarts.de
Tue Jan 24 21:41:05 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.


On Tuesday 24 January 2012 11:14:57 Ted Young wrote:
> > Does anyone have any recommendations with managing a large quantity of
> > hot-swappable drives (e.g. tracking which drives in which bay,
> > managing the DRBD volume pairings, etc.)?
> > 
> > Use LVM on top of the drives themselves and then use logical volumes as
> 
> the DRBD backing devices.
> 
> I see why that would solve the problem.  However, I am concerned that it
> might be overkill.  Most notably, I am concerned about adding an extra layer
> of management and overhead.

This little managment overhead can actually be good for you: If you have X 
drives per machine, put them all in one big volumegroup and use the space of 
X-1 to create logical volumes to mirror with drbd. Now as time goes on, the 
smart-monitoring detects that one of the drives is probably failing soon. You 
react by moving the lvs away from that disk to the spare, take the disk out of 
the vg and out of the chassis, insert a new disk, put it in the vg and if you 
like move the lvs back. All while the system was up and running and without 
drbd complaining.

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.

And if your use case makes use of that, you can stripe the logical volumes 
that make up your drbd for performance enhancements.

Have fun,

Arnold
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