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

[Greg Hellings <greg.hellings@xxxxxxxxxxxx>]

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.

--
Greg


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
>> 
>>   
> 


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