[DRBD-user] drbd performance issue on SATA

François Delpierre francois.delpierre at pivert.org
Sun Jan 1 18:04:18 CET 2012

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


Hi, 

I'm building a very low cost virtualization server for a Non Profit organization using 2 HP workstations (500€ each) (8GB Ram, 1.5TB, QuadCore AMD), Software Proxmox and DRBD for the data replication with dedicated gigabit & cross cable for the replication. 

After setting up the replication (Protocol C), I had catastrophic performances, ( dropping to 30 IOPS after 60s of random writes ). 

I also found a lot of reading, not fully explaining my terrific 30 IOPS on 7200RPM drives, but clearly pointing the necessity to have a battery backed up cache controller to sustain random writes generated by the meta-disk. 

As the hardware makrket did change quite a lot recently, especially towards SSD, I immediately realized that 240GB SSD are half price than a small raid controller, a battery for the cache, and 2 small disks with reasonable performances (10rpm). So, I choose SSD. 

I created 2 partitions on my SSD : 
- 128MB for external meta-disk of my slow SATA partition (750GB) 
- 240GB for a second DRBD resource, with internal meta-disk. 

My questions : 
- Is there some recommendations on a SSD setup ? 
- Why is the external meta-disk that few documented ? I spent more than 1 hour to find the syntax of the directive : 

meta-disk /dev/disk/by-id/scsi-SATA_MKNSSDCR240GB_MKN1146A0000032XXX-part1[0]; 

And it's not clear to my what is the [0] at the end ? 

Regards, 

François Delpierre 

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