“umount is too slow”

A question we see over and over again is

Why is umount so slow? Why does it take so long?

Part of the answer was already given in an earlier blog post; here’s some more explanation. Read more

Mirrored SAN vs. DRBD

Every now and then we get asked “why not simply use a mirrored SAN instead of DRBD”? This post shows some important differences. Read more

“read-balancing” with 8.4.1+

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

Trust, but verify

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

DRBD and the sync rate controller (8.3.9 and above)

The sync-rate controller is used for controlling the used bandwidth during resynchronization (not normal replication); it runs in the SyncTarget state, ie. on the (inconsistent) receiver side. Read more

DRBD causes too much CPU-load

The TL;DR version: don’t use data-integrity-alg in a production setup. Read more

“al-extents” explained

There is quite a bit of confusion about the DRBD configuration value al-extents (activity log extents), so here’s another shot at explaining it. Read more

Make the kernel start write-out earlier

Similar to the recent post about setting the vm.min_free_kbytes value there’s another sysctl that might improve the behaviour: the dirty ratio. Read more