Re: [Xen-users] LVM Read/Write speed <10% drive's normal speed

["Olivier B." <xen.list@xxxxxxxxx>]

Hi,

what mount options do you use on the DomU ?
Under Debian there is xen-tools example with the "sync" mount options : 
if you use it, writes will be really slow.
Olivier

Stephen Hamer a Ãcrit :
> Hello all,
>
> I've been searching through the archives and the internet for a while 
> now, and can't seem to find anything that helps me out. I hope you 
> don't my posting this to both xen-users and linux-lvm simultaneously, 
> but i figured it'd help keep the solution in one place... even though 
> it'll be the same across two places... Anyways:
> My setup is this:
>         Xen 3.3 hypervisor (from the ubuntu repositories)
>         Ubuntu 9.04 server
>         Kernel and module listed here: 
> http://www.infohit.net/blog/post/running-xen-on-ubuntu-intrepid-and-jaunty.html
> The dom0 and domUs in my Xen setup are all Ubuntu 9.04, using that 
> kernel. (I'm not sure if the kernel has something to do with it, so i 
> included it just in case.) All the domUs are set up to use LVM. The 
> dom0 uses a straight ext3 fs on /dev/sda1. The domUs use ext3 fs's 
> within LVMs (using LVM2) set up on /dev/sda5.
> I have noticed a massive file I/O problem on all of my domUs. While I 
> can peak file operations around 100 MB/s within the dom0, I can't get 
> anything more than 3 MB/s read OR write out of a file operation on the 
> domUs. I am using values reported by "iotop" to make this distinction. 
> I'm using both the deployment of a Jboss server and the "dd" command 
> to benchmark this. The Jboss slowdown is how I found this. On the 
> dom0, the server takes 56s to come up. On a domU, the same operation 
> takes 15 minutes.
> It should also be noted that I attempted to change the filesystems to 
> ext2, because I noticed that 'kjournald' was chugging away taking up 
> most of the i/o percentage, but only writing at KB/s! Actually, when I 
> removed the journaling is when the process slowed from 7 minutes to 
> 15. Even without the kjournald there, the java process took forever to 
> load and never wrote more than 3 MB/s.
> I have messed around with the 'blockdev' and 'hdparm' commands (the 
> second of which doesn't even interact with any partition on my 
> computer, lvm or no, instead simply failing with an "input/output 
> error" message), but have had no performance increases after messing 
> around with the read ahead speed of the devices. I also tried the 
> "lvchange -r" command to set the readahead higher. I think there's 
> something else missing here, though.
> I'm fairly fresh to xen, this being only my second installation, and 
> I'm extremely fresh to lvm. I've played with what seems like every 
> option within "xm" and the 'lv*' commands. The LVMs themselves I 
> haven't played with all too much yet, as I don't want to nuke a 
> certain domU before it needs to be used heavily tomorrow. I've already 
> killed a test domU that I brought up just for this.
> -Stephen
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