Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
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. -- : Lars Ellenberg : LINBIT | Your Way to High Availability : DRBD/HA support and consulting http://www.linbit.com DRBD® and LINBIT® are registered trademarks of LINBIT, Austria. __ please don't Cc me, but send to list -- I'm subscribed