Re: [Xen-users] xen disk io performance

[Alexandre Chapellon <a.chapellon@xxxxxxxxx>]

Le 29/11/2011 04:14, George Shuklin a écrit :
> "Very high" and "very slow" sounds like "i pay many buks but got small 
> potion".
> How many IOPS postgre generates from dom0 point of view? (see 
> statistics in vbd/tap device in /sys). How do you did you check netapp 
> storage performance?
I have found I have queries that are putting the system on its knees, 
Some are statistics collection and adding the right index just solved 
the problem. I never looked in /sys on dom0 to get informations about 
iops. Instead I used iostats in domU and it gave me ~ 5000 read/s when 
the statistic collection.
If I compare to what I see in /sys on the dom0 (looking in the stat of 
the dm- block device , not the underlying devices) I see ~ 1200 write/s 
and 100 read/s when thing are ok.
Now I still have one database purge job that mess up perf but i only run 
once a week.... I'll wait next monday to watch after this stat file and 
will send back some values here.
Regards.
> FC is not synonym for 'fast work' and netapp ether can't do magic if 
> postgre creates a thousands of cold random read operations.
> I'll like to propose to starts from stat gathering. At least atop in 
> domU with postgre with enabled logging.
> On 28.11.2011 13:03, Alexandre Chapellon wrote:
> > Hello,
> >
> > I have a setup with several xen 3.2.1 dom0s (debian). Most of the VMs 
> > works nice but I have some load pick problem on some postgresql 
> > instances. PGSQL has been tuned quite nicely I guess, but during some 
> > jobs, IO load is very high and postgres seems really slow.
> > I am using FC LUNs fomr a NetApp SAN (with fast FC 15000t/m disks) 
> > and LVM as follow:
> > FC LUNs are in a volume group (I had new LUNs on the VG when mre 
> > space is needed) and VG is splited across several database servers 
> > (Xen guests) using LVs.
> > So my disk config for my VM look like this:
> >
> > disk =[ 'phy:/dev/xendata/postgresql-syslog:xvdb1:w']
> >
> > What can be done to improve disk IO and throuput?
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--
<http://www.horoa.net>

Alexandre Chapellon

Ingénierie des systèmes open sources et réseaux.
Follow me on twitter: @alxgomz <http://www.twitter.com/alxgomz>


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