A question we see over and over again is
Why is
umountso slow? Why does it take so long?
Part of the answer was already given in an earlier blog post; here’s some more explanation. Continue reading
“umount is too slow”
Reply
Tag Archives: kernel
Raspberry Tau: a Pi cluster
The Raspberry PI is a small ARM computer (hardware specifications in wiki, outline and FAQs). Of course, you can build a cluster with it! Continue reading
“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. Continue reading
Monitoring: better safe than sorry…
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 accept1
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 anymore2; 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. Continue reading
Maximum volume size on DRBD
From time to time we get asked things like this:
I want to use a 10TiB volume with DRBD, is that supported”?
The easiest way to answer things like that is to say look for yourself on the public DRBD usage page – the biggest public device size is ~220TiB, so go figure 
Continue reading
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 Verify1 it might be a good idea to periodically test whether the nodes really have identical data, similar to the checks that are2 done for RAID sets. Continue reading
DRBD causes too much CPU-load
The TL;DR version: don’t use data-integrity-alg in a production setup. Continue reading
Increase vm.min_free_kbytes for better OOM resistance
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! Continue reading