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