[DRBD-user] Choosing right combination of md-raid, LVM and DRBD

H.D. devnull at deleted.on.request
Thu Sep 27 16:53:37 CEST 2007

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

On 27.09.2007 16:27, Rustedt, Florian wrote:
> MD-Raid mirror on the disks per server, then LVM ontop and then DRBD on the
> resulting partititions? Or LVM -> RAID -> DRBD?

At least if you plan to use proto C and care about performance, I 
consider it essential to have a battery backed hardware controller and 
to not use soft raid. It's much faster to commit a changed block to 
controller cache than to physical media.

> And what is the right setup for the partitions?
> The ideal-case would be, that both systems are able to boot the same data
> from scratch, but i saw in the list and google, that most systems do NOT
> use DRBD for the root-partition? Why not? Isn't it stable enough?

Well, first you'd need at least an initrd for it, second I don't think 
it's a good idea to boot two identical systems. The systems would need 
to get their IP addresses and config from DHCP.

> So what is the best way to partition tihs beast? And why?
> And is basically LVM a good choice or does it have a remarkable impact on
> performance, so it would be better, to keep rid of it?

It has a measurable impact. It depends on type of load and the hardware, 
but I consider it negligible. About 4-6% for PostgreSQL OLTP load on top 
of HW Raid 10 - to give you an idea.


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