WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-users

RE: [Xen-users] Disk IO trouble in Xen

To: "Greg Hellings" <greg.hellings@xxxxxxxxxxxx>, <xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-users] Disk IO trouble in Xen
From: "Ross S. W. Walker" <rwalker@xxxxxxxxxxxxx>
Date: Mon, 5 May 2008 17:58:13 -0400
Delivery-date: Mon, 05 May 2008 14:59:15 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
Importance: normal
In-reply-to: <C444CE33.11BB1%greg.hellings@xxxxxxxxxxxx>
List-help: <mailto:xen-users-request@lists.xensource.com?subject=help>
List-id: Xen user discussion <xen-users.lists.xensource.com>
List-post: <mailto:xen-users@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-users>, <mailto:xen-users-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-users>, <mailto:xen-users-request@lists.xensource.com?subject=unsubscribe>
Priority: normal
References: <481AF557.7030901@xxxxxxxxxx> <C444CE33.11BB1%greg.hellings@xxxxxxxxxxxx>
Sender: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: Aciu+W7brUb+EBrsEd2umQAX8t0tvQAAWDiw
Thread-topic: [Xen-users] Disk IO trouble in Xen
Greg Hellings wrote:
> 
> I started this thinking I was having an IO problem.  Now, I'm 
> not so sure.
> I am using a pre-allocated disk, not a sparse file.
> 
> Write performance seems about the same for both
> 
> Dom0
> [root@localhost ~]# dd if=/dev/zero of=/tmp/dummy count=2097152
> 2097152+0 records in
> 2097152+0 records out
> 1073741824 bytes (1.1 GB) copied, 29.8368 seconds, 36.0 MB/s
> 
> DomU
> [root@localhost ~]# dd if=/dev/zero of=/tmp/dummy count=2097152
> 2097152+0 records in
> 2097152+0 records out
> 1073741824 bytes (1.1 GB) copied, 30.4716 seconds, 35.2 MB/s
> 
> Iozone shows very similar numbers on both the Dom0 and DomU. The DomU seems
> to freeze periodically and drop network connections.  I assumed this was IO
> related because everything else seems fine and those hdparm numbers are so
> far off.  Also heavy IO related tasks seem slow.  I'm fairly baffled now.
> 

Run a 'vmstat 1' and take a look at the interrupts and io waits.

Maybe the network is generating a high load?

Performance, and performance under load are two different things.


> On 5/2/08 4:04 AM, "Sadique Puthen" <sputhenp@xxxxxxxxxx> wrote:
> 
> > Are you using a pre-allocated image or a sparse file? If 
> the latter it's
> > likely to have performance problems like you found?  What 
> if you test
> > with dd or iozone or bonnie++?
> > 
> > --Sadique
> > 
> > Greg Hellings wrote:
> >> I'm having terrible IO trouble with an image based domu
> >> 
> >> 
> >> This is the performance on the Dom0
> >> [root@localhost /]# hdparm -tT /dev/sda
> >> 
> >> /dev/sda:
> >>  Timing cached reads:   3228 MB in  2.00 seconds = 1617.22 MB/sec
> >>  Timing buffered disk reads:  174 MB in  3.02 seconds =  
> 57.60 MB/sec
> >> 
> >> 
> >> And this is the performance on the DomU
> >> [root@localhost ~]# hdparm -tT /dev/xvda
> >> 
> >> /dev/xvda:
> >>  Timing cached reads:   3336 MB in  2.00 seconds = 1669.98 MB/sec
> >>  Timing buffered disk reads:   26 MB in  3.13 seconds =   
> 8.30 MB/sec
> >> 
> >> 
> >> Is it normal for the performance difference to be so 
> great?  I'm running
> >> CentOS 5 and the DomU image is stored on a LVM ReiserFS 
> formatted partition.
> >> 
> >> Here is the config for the DomU
> >> name = "dddevdb"
> >> uuid = "927f1e915813c2dec60c8f76c2716783"
> >> maxmem = 3072
> >> memory = 2042
> >> vcpus = 2
> >> bootloader = "/usr/bin/pygrub"
> >> on_poweroff = "destroy"
> >> on_reboot = "restart"
> >> on_crash = "restart"
> >> vfb = [ "type=vnc,vncunused=1,keymap=en-us" ]
> >> disk = [ "tap:aio:/var/lib/xen/images/dddevdb.img,xvda,w"]
> >> vif = [ "mac=00:16:3e:62:7a:d1,bridge=xenbr0" ]
> >> 
> >> 
> >> _______________________________________________
> >> Xen-users mailing list
> >> Xen-users@xxxxxxxxxxxxxxxxxxx
> >> http://lists.xensource.com/xen-users
> >> 
> >>   
> > 
> 
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users
> 

______________________________________________________________________
This e-mail, and any attachments thereto, is intended only for use by
the addressee(s) named herein and may contain legally privileged
and/or confidential information. If you are not the intended recipient
of this e-mail, you are hereby notified that any dissemination,
distribution or copying of this e-mail, and any attachments thereto,
is strictly prohibited. If you have received this e-mail in error,
please immediately notify the sender and permanently delete the
original and any copy or printout thereof.


_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users