29.09.2016 09:21, Michael Rasmussen пишет:
On Thu, 29 Sep 2016 09:17:56 +0300
Dmitry Petuhov <mityapetu...@gmail.com> wrote:
It's side effect of scsi pass-through, which is being used by default for
[libi]scsi volumes with scsi VM disk interface. QEMU is just not aware of VM
block IO in that case. Also, cache settings for volumes are ineffective,
because qemu is just proxying raw scsi commands to backing storage, so caching
is impossible.
Do you use PVE backups (vzdump)? Is it works for machines without stats? I
think it's also shall not work with pass-through.
What do you mean by pass-through? (no pass-through is happening here
since the storage resides on a SAN)
In QemuServer.pm (some code omitted):
if ($drive->{interface} eq 'scsi')
my $devicetype = 'hd';
if($path =~ m/^iscsi\:\/\//){
$devicetype = 'generic';
}
$device = "scsi-$devicetype ...
So usually if drive interface is scsi, PVE uses fully-emulated qemu
device 'scsi-hd'. But for iscsi: volumes (iscsi direct and zfs over
iscsi) it uses 'scsi-generic' device, which just proxies scsi commands
between guest OS and your SAN's iscsi target.
BTW, I began write code to on|off pass-through in storage's config, so
that we could force it off, even if it can be used. If developers are
interested, I can find it.
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