[DRBD-user] Multi-disk devices possible?

Sebastian spa at syntec.co.uk
Fri Jun 3 13:55:29 CEST 2011

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


Felix Frank wrote:
> On 06/03/2011 12:26 PM, Sebastian wrote:
>> Do you think I would see much performance benefit
>> from running my O/S (see next para for details) directly on the bare
>> metal? 
> 
> I have no idea. Disk I/O is generally the bottleneck in virtualization
> setups, but DRBD overhead usually has much to do with network latency
> and throughput, which in turn are supposed to virtualize quite well.
> 
> So, if you're facing performance issues, you may want to do
> some tests,
> but I don't see an immediate need to loose the virtualization layer.

OK, performance is not our main concern here, so it seems OK for now.

>> /dev/sdb2 ~ 1 TB - /dev/drbd1 (actually LVM so
>> /dev/mapper/vg0drbd-filer) - used for NAS /dev/sdc1 ~ 1 TB -
>> /dev/mapper/tempnas-tempnasv LV 
> 
> Is DRBD on top of LVM or vice versa?
> If DRBD is on top, you should have an easy ride indeed.

No, LVM is on top of DRBD (although there is only 1 LV currently
configured).

>> What would be the benefits and
>> disadvantages of splitting 1 mounted LV filesystem over 2 DRBD
>> devices? 
> 
> You mean, create two DRBDs, make both LVM PVs and have an LV
> span both?

Yes.

> Don't. Just don't. Imagine an FS that depends on two
> resources that can
> each indepentently be available on only one of your HA nodes.
> Don't put
> yourself into this position.

Good point. Back to your plan then!

>> When you say "scrub", I presume that is
>> optional?
> 
> It is.
> 
> HTH,
> Felix

Thanks, I will get started on putting DRBD on an LVM then...

Kind regards,

Sebastian




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