[DRBD-user] Persistent Device Names

Ted Young mail at tedyoung.me
Tue Jan 24 23:50:09 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.


> 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






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