Hi Jan, Am Dienstag, den 10.10.2017, 06:56 +1300 schrieb Jan Bakuwel: > I've seen OOS blocks in the past where storage stack appeared to be fine > (hardware wise). What possible causes could there be? Hardware issues, bugs > in storage stack including DRBD itself, network issues. In most (all?) cases > it seems prudent to me to keep the resources in sync as much as possible and > of course investigate once alerted by the monitoring system.
a common configuration issue is using O_DIRECT for opening files or block devices. O_DIRECT is used by userspace processes to bypass parts of the kernel's I/O stack with the goal to reduce CPU cycles required for I/O operations and to eliminate/minimize caching effects. Unfortunately this also allows the content of buffers to be changed while they are still "in-flight", speaking simplified, e.g. while being read/mirrored by DRBD, software RAID, ... The general use for O_DIRECT is for applications that either want to bypass caching, such as benchmarks, or that implement caching by themselves, which is the case for e.g. some DBMS. But also qemu (as used by KVM and Xen) implements several kinds of caching and uses O_DIRECT for VM disks depending on the configured caching mode. HtH, // Veit _______________________________________________ drbd-user mailing list [email protected] http://lists.linbit.com/mailman/listinfo/drbd-user
