Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On 11/07/11 22:07, Mark Dokter wrote: > On 7/11/11 4:21 PM, Phil Stoneman wrote: >> I think that LVM that comes with recent kernels support barriers, which >> is why you're seeing this. > > How recent? I'm using the 18.104.22.168 xen-stable git tree from > git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git According to http://en.wikipedia.org/wiki/Logical_Volume_Manager_%28Linux%29#Caveats, write barriers in LVM were sort-of-supported from 2.6.31, and fully supported from 2.6.33. >> Or, to put it another way: I have good and regularly tested backups; the >> small risk of losing a bit of data on writes is more than offset by the >> massive speed benefit that no-disk-barrier and no-disk-flushes gives me. >> > > We've got a regular backup on tape, but that doesn't cover system > partitions of the virtual machines. So the issue is the downtime, not > the loss of data, if a partition gets corrupted :( In our case, we want the advantages that drbd brings, but the department using that server (which is actually a KVM virtual machine) will notice if the performance is an order of magnitude worse than using local disks - which it sadly seems to be under some test conditions when using barriers :( Phil