[DRBD-user] Limit Syncer Speed

Adam Goryachev mailinglists at websitemanagers.com.au
Thu Dec 15 04:06:31 CET 2016

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On 15/12/16 13:48, Jasmin J. wrote:
> Hello Lars!
> > Maybe this nice post from 2012,
> > helps to realize what congestion is?
> > Pasted here for your convenience, even though it is in the archives.
> THX for answering, it explained it pretty good.
> > But even with massive buffers (funnels),
> > the sustained mid term/long term average write rate
> > obviously cannot exceed the minimum bandwith within the whole system.
> This depends how you implement Protocol A. It seems that it slows down 
> the
> write speed when the "funnel" is full. It seems the main goal is to keep
> both in sync, even if this costs write speed.
> The original from 2012 poster asked this:
> >> I was expecting that if I switched to protocol A, I would be able 
> to let
> >> the SSD drive write at it's full speed (e.g. 250MB/s) only at the 
> price of
> >> the secondary potentially falling a little bit behind
> I guess he meant here the peer going out of sync.
> I know (because of the explanation) it isn't implemented that way. But
> wouldn't it be possible to implement Protocol A2 (or D), which simply 
> writes
> with full speed to the local disk regardless if the peer can follow, 
> get out
> of sync and let the already implemented sync mechanism resync the peer 
> with
> the configured sync parameter settings during the heavy write load and
> also continue syncing until it is consistent again?
> There is already a bitmap of inconsistent blocks implemented. Instead of
> trying to update the peer with each write the driver could simply set 
> the bit
> in the bitmap, if the buffer (funnel) gets full and change back to the 
> already
> implemented sync mode (which is currently used only after a peer 
> connecting again).
I would advise that you refer to the documentation, what you are asking 
for already exists:
Specifically look for |on-congestion|


Adam Goryachev Website Managers www.websitemanagers.com.au
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