On Sun, 13 Feb 2011 11:01:43 +1100 Eyal Lebedinsky <eyal@xxxxxxxxxxxxxx> wrote: > I have scripts that do a raid check, then proceed to identify any files > affected. I then manually deal with these. > > I have a few issues with this RADI6 setup, here is one. > > I am setting sync_min and sync_max, start a check and wait for sync_completed > to equal sync_max. > > I assumed that when equal it means that this address was "completed". After > doing this for a while I observed that this is probably not the case. > > My expectation is that sync_completed has 'none' until it finished a chunk. > It then updates it with later completed ones. When it reaches sync_max > it pauses, and I then raise sync_max for the next area. This way I can > tell where a mismatch occurs. If sync_completed is set before a chunk > is completed then I may fetch mismatch_cnt too early (while the last > chunk is still being checked). This seems to be the case. > > Q: Is this the case? The intention of sync_completed is that it is only updated after sync/check/repair/recovery has actually completed to that point. It may be updated well *after* the sync has happened, but should never be updated *before*. However it is entirely possible that the code is not 100% correct. If you give me details of what you are seeing together with precise kernel version number I can try to explain them for you. > > Setting ranges that are too small (minimum is 1024) makes the check > *very* slow. I notice that ranges of 1m or even 4m are required to > get the check to move along close to the maximum speed. > > Q: Does the check take time to speed up rather than immediately go at > the nominated sync_speed_max rate? This is almost certainly an artifact of the way disk drives work. To get streaming reads from a disk drive you need to request at least a whole cylinder at a time. As cylinders differ in size, it really only works if you request multiple cylinders at a time. I don't know how big cylinders are these days but I suspect they are a few hundred K to a Meg. So needing 4M at a time to get streaming happening doesn't surprise me at all. 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
