[DRBD-user] Two newbie questions

Ben Beuchler insyte at gmail.com
Wed Aug 4 21:10:39 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.

> system can block-write. I'm interested in why the active-backup
> recommendation, and other folks' experiences with bonding.

My recollection from Florian Haas' presentation:

Bonding works well when you have UDP traffic or multiple TCP streams.
However when you push a single TCP stream across a bonded ethernet
link, the remote end gets bogged down handling the out-of-order
packets and your overall throughput can actually *decrease*.  My notes
indicate that their experimenting showed that adding a second bonded
ethernet link resulted in about a 60% increase in throughput.  Adding
a third link dropped throughput to the same as a single link.

> (2) System A (primary) and system B (secondary). If B is shut down, A
> maintains a list of out-of-sync blocks for B. Where is this kept?

In the system A's metadata.

> If in the
> metadata (internal), how often is it updated on disk?

With each write.  Marking the block "dirty" is completed before the
write() call is allowed to return.

> If A is shut down and rebooted before B comes alive, any chance of losing any updates?

Not under normal circumstances.  I'm sure someone will promptly
respond with a scenario that could cause data loss...


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