Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Hello, Thank you for fast reply. 2011/8/18 Lars Ellenberg <lars.ellenberg at linbit.com>: > On Thu, Aug 18, 2011 at 11:18:52AM +0200, Łukasz Oleś wrote: >> Hello, >> >> Can someone explain me what is the difference between those two >> parameters(rate and c-min-rate)? >> Is it good idea to set same value to them? > > rate (sync-rate, resync-rate) is the upper limit for the rate the resync > process tries to achieve, when NOT using the "dynamic resync rate > controller", introduced in recent drbd versions (recomended: >= 8.3.11 > respectively 8.4) > > To enable the dynamic resync rate controller, set c-plan-ahead to some > non zero value; defaults to 0 (off) in 8.3, and to 20 (enabled) in 8.4. > > If enabled, the resync-rate parameter is only used as initial guess > value, and otherwise pretty much ignored. > > This controller basically tries to use as much as c-max-rate bandwidth, > but will automatically throttle, if > - application IO on the device is detected (READ or WRITE), > AND the estimated current resync speed is above c-min-rate > (where c-min-rate = 0 disables this particular throttling condition) > - the amount of in-flight resync requests exceeds c-fill-target > - the estimated peer response latency exceeds c-delay-target > > Where only one of the conditions of c-fill-target and c-delay-target is > used. If c-fill-target is non-zero, it will be used. If c-fill-target is > set to 0, c-delay-target is used. > > c-plan-ahead gives something like the "dampening interval" of the controller, > that is how fast it will ramp up/down. > > This is all to try to get as much as possible out of the way of > application IO, to lessen the impact of the resync on > application IO latencies, while still trying to use up as much > "idle bandwidth" as possible. > > There is a short paragraph about it in the drbdsetup man page, > and an example use case in the DRBD User's Guide. I already read documentation. I'm using drbd 8.3.10. Dynamic resync rate controller is disabled. I configured rate option to 40MB but when application started writing data resync speed droped to 4MB. To change it I had to set c-min-rate to 40MB as well. It looks like c-min-rate works even if dynamic resync rate controller is disabled. This is why I'm asking about diffrences. I should clarify it in first e-mail, sorry for that. Regards, -- Łukasz Oleś