[DRBD-user] sync data size of DRBD

Florian Haas f.g.haas at gmx.net
Fri Sep 23 10:57:37 CEST 2011

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

On 2011-09-23 10:09, Lyre wrote:
> Hi all:
> Want to know the sync data size of DRBD.
> If application write 1 bytes to a drbd device, how may datas will be
> write to another node? In this 2 scenarios:
> 1. Both nodes are connected (UpToDate/UpToDate).

Whatever the minimum chunk is that your application writes do the block
device. If you have, say, a block based filesystem such as ext3, and
your block size is set to 4K, then the block device is always going to
be written to in blocks of 4K. And DRBD will replicate that. That is
nothing within DRBD's control though.

If you have an application (or filesystem) that writes to its block
device in smaller increments, then DRBD will happily replicate those
smaller increments too. It's generally a fairly safe bet, though, that
filesystems won't attempt to write chunks of data that are smaller than
the hard sector size of the underlying physical block device (normally
either 512 bytes or 4K).

> 2. background resync.

Increments of 4K.

> In a oracle case, we have file size increased about 135MB, but DRBD
> have to transmit about 1GB, is that something wrong?

Eh, what? How did you arrive at those numbers, IOW, what makes you think
DRBD is transmitting 1G, and in what context?

And also, do you have a name? It's rather uncommon on this last to post
from a non-identifiable GMail address and also to never give one's name
in a signature.


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