[DRBD-user] drbd+lvm sizing and performance

Eric Robinson factcheck_1776 at yahoo.com
Fri Sep 26 14:14:32 CEST 2008

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

Hi all,
I have a pair of new servers, each with 6x300GB 15K SAS drives configured as a 1.1TB (usable) RAID5 array. The servers will be a heartbeat+drbd active/active cluster. One server will be primary for MySQL and the other server primary for FTP. 
My old servers have about 60GB of MySQL data and 140GB of FTP files (average size about 80K). On the new servers, DRBD will ride on top of LVM. I want to allocate 200GB for MySQL data as LV01 and 400GB for FTP data as LV02, leaving about 500GB unallocated and available for future needs. 
Here are my questions:
1. If I create LV01 with 200GB and LV02 with 400GB, and then later I grow LV01 by another 200GB, should I expect performance issues with drbd caused by the separation of LV01's PVs on the disk platters? In terms of performance, would it be better to allocate the maximum expected size at the beginning and give up flexibility later?
2. I assume DRBD does not care if, when, or how its backing devices are grown, and that I can issue an lvextend command on an LVM that is being used as a DRBD backing device without expecting any problems. This can be done during production hours. Is this correct?
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