On Tue, 24 May 2022, Christoph Hellwig wrote: > 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 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 :( Thanks for the feedback, great info! In your experience, which SAS/SATA RAID controllers are best behaved in terms of policies and reporting things like io_opt and writeback/writethrough to the kernel?
