On Tue, May 24, 2022 at 02:34:23PM -0700, Eric Wheeler wrote: > Is this flag influced at all when /sys/block/sdX/queue/scheduler is set > to "none", or does the write_cache flag operate independently of the > selected scheduler? This in completely independent from sthe scheduler. > Does the block layer stop sending flushes at the first device in the stack > that is set to "write back"? For example, if a device mapper target is > writeback will it strip flushes on the way to the backing device? This is up to the stacking driver. dm and tend to pass through flushes where needed. > This confirms what I have suspected all along: We have an LSI MegaRAID > SAS-3516 where the write policy is "write back" in the LUN, but the cache > is flagged in Linux as write-through: > > ]# cat /sys/block/sdb/queue/write_cache > write through > > I guess this is the correct place to adjust that behavior! MegaRAID has had all kinds of unsafe policies in the past unfortunately. I'm not even sure all of them could pass through flushes properly if we asked them to :(
