[DRBD-user] Large block IO bottleneck

Ross S. W. Walker rwalker at medallion.com
Thu Jan 4 18:00:11 CET 2007

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

> -----Original Message-----
> From: drbd-user-bounces at lists.linbit.com 
> [mailto:drbd-user-bounces at lists.linbit.com] On Behalf Of 
> Leroy van Logchem
> Sent: Thursday, January 04, 2007 3:58 AM
> To: drbd-user at lists.linbit.com
> Subject: Re: [DRBD-user] Large block IO bottleneck
> >>>> Hi there I am using DRBD 0.7.21 with iSCSI Enterprise
> >>>>         
> > The 32k are a rather arbitrary value we have chosen in 
> DRBD. Such a limit
> > is needed for some of the algorithms in the area of the two primary
> > nodes, write conflict detection code.
> >
> > If you really want you can change that define (HT_SHIFT), 
> but probably
> > the positive effects are out-numbered by negative effects 
> (more collision
> > in hash tables etc...)
> >   
> I was hoping to analyse the difference by patching the source but the 
> HT_SHIFT define
> is only used in the 8.x code. What would need changing to try 
> 32K BIO's 
> in the 0.7.x code?

You can try, but I think you will find that the internal meta-data
expects to handle certain sized BIOs and there will need to be other
parameters that need changing and the outcome will be dubious as the
performance is tuned for the current BIO size.

Let me know though if you do and what happens.


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