XenServer and DRBD
While XenServer and DRBD do play together nicely in various setups, problems can be encountered when using a setup similar to this:
sda3 -> LVM -> DRBD -> LVM -> LVM
This occured in a complex XenServer setup we were building.
When booting the (paravirtualised) guest we saw this message in the systems log:
kernel: drbd6: bio would need to, but cannot, be split: (vcnt=4,idx=0,size=4096,sector=4423615)
Simultaniously the guest would complain about unreadable sectors on the drive.
The issue is actually rather simple, and documented on the internet.
But while some xensource users switch over to file-based VM’s as a work-around, this is not an option in XenServer.
So, how can this really be solved?
By simply adding an extra parameter to the drbd.conf:
disk {
max-bio-bvecs 1;
}
This simple switch effectively cures the whole situation.
If you want more information about this switch, please read the man files on drbd.conf
man drbd.conf
The switch and what it does is fairly well documented there.
Tags: Citrix XenServer, DRBD, hosting, Linux, servers
