On Monday November 12, davidsen@xxxxxxx wrote: > Neil Brown wrote: > > > > However there is value in regularly updating the bitmap, so add code > > to periodically pause while all pending sync requests complete, then > > update the bitmap. Doing this only every few seconds (the same as the > > bitmap update time) does not notciable affect resync performance. > > > > I wonder if a minimum time and minimum number of stripes would be > better. If a resync is going slowly because it's going over a slow link > to iSCSI, nbd, or a box of cheap drives fed off a single USB port, just > writing the updated bitmap may represent as much data as has been > resynced in the time slice. > > Not a suggestion, but a request for your thoughts on that. Thanks for your thoughts. Choosing how often to update the bitmap during a sync is certainly not trivial. In different situations, different requirements might rule. I chose to base it on time, and particularly on the time we already have for "how soon to write back clean bits to the bitmap" because it is fairly easy to users to understand the implications (if I set the time to 30 seconds, then I might have to repeat 30second of resync) and it is already configurable (via the "--delay" option to --create --bitmap). Presumably if someone has a very slow system and wanted to use bitmaps, they would set --delay relatively large to reduce the cost and still provide significant benefits. This would effect both normal clean-bit writeback and during-resync clean-bit-writeback. Hope that clarifies my approach. Thanks, NeilBrown - 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
