Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
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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>> drbd-user at lists.linbit.com
>> http://lists.linbit.com/mailman/listinfo/drbd-user
>>
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