On 02/03/2015 07:49 PM, Roger Heflin wrote: > In general if you completely disable write caching things will likely > be unusable. When I have benchmarked things attempting to turn off > write cache performance has been mostly unusable. > > I usually change /etc/sysctl.conf and change these entries to control > the amount of dirty cache. > > vm.dirty_background_bytes = 25000000 > vm.dirty_bytes = 50000000 > > That says max dirty allowed is 50mb, and it syncs down to 25mb when it syncs. Er, where do you have this from? dirty_background_bytes and dirty_bytes are more about non-blocking and blocking dirty writes. And about the amount of dirty data that triggers it (i.e. there is no need to flush temporary file data to disk if files get immediately deleted after writing them) linux/Documentation/sysctl/vm.txt ============================================================== dirty_background_bytes Contains the amount of dirty memory at which the background kernel flusher threads will start writeback. Note: dirty_background_bytes is the counterpart of dirty_background_ratio. Only one of them may be specified at a time. When one sysctl is written it is immediately taken into account to evaluate the dirty memory limits and the other appears as 0 when read. ============================================================== ============================================================== dirty_bytes Contains the amount of dirty memory at which a process generating disk writes will itself start writeback. Note: dirty_bytes is the counterpart of dirty_ratio. Only one of them may be specified at a time. When one sysctl is written it is immediately taken into account to evaluate the dirty memory limits and the other appears as 0 when read. Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any value lower than this limit will be ignored and the old configuration will be retained. ============================================================== Bernd -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
