[DRBD-user] DRBD on top of LVM - 50% performace drop

Digimer linux at alteeve.com
Fri Sep 10 15:19:31 CEST 2010

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

On 10-09-10 08:06 AM, trekker.dk at abclinuxu.cz wrote:
> As I mentioned, I tested DRBD in _standalone_ mode - without network
> connection - so I don't need to take any network-related latencies into
> account.
> The only thing added on top of LVM (and all those other layers) here is
> the DRBD layer, which doesn't need to wait on network and (in my
> opinion) should be passing requests to lower layers as quickly as possible.

Dan's comment about Protocol is important. With Protocol C, DRBD will
not return a successful write to the OS until the data has been written
to disk on both nodes. Without the other node there, you could be seeing
slowdown caused by DRBD waiting, and then giving up, for communication
with the other disconnected node.

Re-run your tests with Protocol A. Of course, as Dan pointed out, this
is not normally safe. However, if you're rarely ever going to have the
other node connected...

As an aside, have you considered simply freezing and dd'ing your VM when
you want to migrate it? It doesn't seem like you really need DRBD if
you're not concerned about keeping the data sync'ed across two nodes.

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