[DRBD-user] write performance issues
pws at corefiling.com
Tue Jul 12 09:38:16 CEST 2011
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 184.108.40.206 xen-stable git tree from
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
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