[DRBD-user] Some questions about drbd

Lars Marowsky-Bree lmb at suse.de
Wed Jul 6 15:27:33 CEST 2005

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

On 2005-07-06T11:22:09, Sven Schuster <schuster.sven at gmx.de> wrote:

> 1. When the secondary node is down for some time, no mirrored
>    hard disk is replaced, how will it be re-synced when it comes
>    up again?? Will a complete resync take place, or just the
>    changed parts of the block device? If just the changed parts
>    are synced, how are those changed parts determined, and what
>    is the order in which those parts are synced?? Would such a
>    partial resync retain transactions as done by applications??

With 0.7 onwards, only the modified parts are synced, which are tracked
in a combination of an activity log and a bitmap structure.

During the resync, which basically works from the beginning of the disk
to the end, the secondary will be "inconsistent" for a short period of

> 2. drbd is independent from the kind of block device which is
>    underneath it, right?? So, as long as the kernel itself can
>    use a block device, it can be used by drbd, regardless if it's
>    an ide drive, scsi, raid, or maybe even a ramdisk :-)


> 3. are there any pitfalls in using drbd on top of hardware raid?


> 4. one of the questions that came to my boss' mind and which is
>    (more or less) directed to linbit: is there any guarantee that
>    drbd will still exist in, say, 5 to 10 years from now?? What I
>    mean is, if we use it at work, we well use it for quite some
>    time and have to make sure that it isn't gone in two years...
>    (please bear with me, I've been using linux for about 10 years
>    now, I'm an open source freak, but my boss is not...and I'd like
>    my opinions to be backed up by someone more knowledgeable, at best
>    by someone from linbit :-) )

Well, first, this is Open Source - so even if drbd was "dropped", if you
had enough incentive, you could revive it. Also, given that the data is
1:1 on the disk, with just some additional data for drbd housekeeping at
the end of the drive, you can easily get access to it.


Second, you can purchase a drbd support & maintenance contract from

Third, if you ask such a question, I'm inclined to point out that the
SUSE Linux Enterprise Server 9 ships with drbd 0.7 and will be
maintained for a couple of more years (I think 5), and SLES10 will also
include drbd and will be maintained for a couple of years too. Then the
question becomes: How likely is it for Novell to disappear and not
fulfill the support committment? Maybe that makes your boss more happy.


    Lars Marowsky-Brée <lmb at suse.de>

High Availability & Clustering
SUSE Labs, Research and Development
SUSE LINUX Products GmbH - A Novell Business	 -- Charles Darwin
"Ignorance more frequently begets confidence than does knowledge"

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