[DRBD-user] memory requirements for DRBD

[Lars Ellenberg]

On Fri, Jan 23, 2009 at 05:59:47PM +0100, Bruno Voigt wrote:
> Hi,
> 
> I'm looking for some figures:
> 
> What are the memory requirements/guidelines for DRBD resources?
> What are the maxima for normal operation, sync, verify ?
> Is it dependent on the size of the replicated device?
> Does the requirements increase lineary with each resource ?
> 
> I'm playing with a Debian lenny/unstable system pair (HP DL360 G5, 8G RAM)
> with linux 2.6.18.6 (or 2.6.26.1), xen 3.2.1, DRBD 8.3.0,
> hosting 13 DomU - each with 2 DRBD-Devices (4G disk+512M swap)
> allocated from LVM LVs each separately replicated with DRBD.
> 
> The Dom0 got a fixed amount of memory (1 G via grub menu.list
> xenhopt=dom0_mem=1024M)
> and I've seen the situation that the Out-of-memory killer strikes on the
> node A
> if all DRBD resources are synced (all at once) from node A to  initially
> connected node B.
> 
> Nothing else besides an small apache is running on the Dom0,
> in disconnected mode there is over 600M available on node a.
> 
> If I sync the resources one by one the OOM can be prevented.
> 
> So I'm looking for a solid based way to size the RAM of the Dom0 ..

From: Lars Ellenberg
Subject: Re: Summarizing DRBD memory usage
Date: 2008-07-24 10:43:52 GMT
http://thread.gmane.org/gmane.linux.network.drbd/15482/focus=15485

so in your situation,
right, serialize the resync (probably a good idea anyways).
and/or maybe decrease "max-buffers", which limits the number of
in-flight pages.

or give it plenty of ram.

-- 
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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