I'm going to stop in the office tonight and try doing some upgrades.
1.5MB write is killing my system when someone tries to write out a non
trivial file. My guess is the load goes up as the write gets queued
since the write is way to slow.
Ken
On 07/10/2011 04:26 PM, Zev Weiss wrote:
Hi,
There seems to be a number of people experiencing this problem (myself
included). I've only seen one response offering any sort of suggestions so far
(http://article.gmane.org/gmane.comp.linux.drbd/22060), but I tried changing my
configuration to more closely match what Ulrich mentioned in that message and
saw no change in performance.
It would be great if a developer (or someone with a similar level of
expertise/authority) could chime in on this, but I haven't seen that happen yet.
Please do post to the list if you find a solution!
Thanks,
Zev
On Jul 8, 2011, at 8:00 AM, Mark Dokter wrote:
Hello!
I have a rather complex setup and experience severe performance
degradation, especially on small writes.
------------------------------------
The scenario:
- Two xen servers with:
- kernel 2.6.32 (xen-stable git)
- xen 4.1.0
- ubuntu 11.04
- backported drbd 8.3.7
- domUs using pv-on-hvm drivers
- DRBD volumes for the domUs:
HW RAID6 -> LVM -> DRBD
- Sync Network:
- dedicated 1Gbit/s ethernet (switched)
- DRBD volume config:
resource pegasus {
device /dev/drbd8;
disk /dev/data/pegasus;
meta-disk /dev/data/drbd-metadata[8];
net {
allow-two-primaries;
max-buffers 8000;
max-epoch-size 8000;
sndbuf-size 0;
unplug-watermark 16;
}
syncer {
al-extents 3389;
rate 110M;
}
on xen01 {
address 172.16.128.1:7797;
}
on xen02 {
address 172.16.128.2:7797;
}
}
------------------------------------
I have several domUs set up like this. The worst slowdowns are with
- mailserver (postfix/cyrus)
- mysql
- copying a lot of small files
A small test I ran(disk/net i/o checked with dstat):
- copied the mailman directory (110 lists, 6.5 GB of data)
cp -a mailman mailman-backup
- after about 15 minutes I had a look how far the copying got:
about 1 GB copied.
- in the dom0 there was about 1 MB/s traffic on the sync network.
Same speeds as the disk write performance in the domU
- I disconnected the DRBD volume on the second xen dom0
(the one the virtual machine was not running on)
drbdadm down pegasus
- the disk write performance in the domU went up to around 30 - 40 MB/s
The 30-40 MB/s aren't really fast either, but that'd be bearable. When I
reconnected the volume after the copying was done, the resync went quite
fast (also with those 30 - 40 MB/s).
I know, the numbers aren't that exact, but it's enough to see the big
difference when the DRBD volumes are in connected/disconnected state.
I already did quite some research on that issue (that's how I came up
with that DRBD config), but didn't succeed in fixing it. Maybe someone
on this list has suggestions?
Thanks,
Mark
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