DRBD 8.4.1 introduces a new feature:
read-balancing, which is configured in the
disk section of the configuration file(s). This feature enables DRBD to balance read requests between the Primary/Secondary nodes. Read more
Stumbling upon the Holy time-travellin’ DRBD, batman! blog post there’s only one thing to be said …
Be strict in what you emit, liberal in what you accept[1. Thanks, Larry]
is simply not true when dealing with mission-critical systems.
It’s ok to be alerted on upgrading a machine because the “old, working” RegEx that did the parsing doesn’t match anymore[1. eg. because
/proc/drbd got an additional field]; it’s not a problem to get an email when someone adds the 100th DRBD resource and causes the grep to fail; and so on. Read more
DRBD tries to ensure data integrity across different computers, and it’s quite good at it.
But, as per the old saying Trust, But Verify[1. attributed either to Lenin or Kennedy] it might be a good idea to periodically test whether the nodes really have identical data, similar to the checks that are[1. or at least can be] done for RAID sets. Read more
The TL;DR version: don’t use
data-integrity-alg in a production setup. Read more
Depending on your setup and your workload (eg. within a virtual machine with little memory and much I/O) you could get into the situation that the kernel has little memory left, so wants to write some dirty pages to disk, but cannot, because for that it would need some memory free! Read more