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 2.6.32.41 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
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